Welcome to Plbg.com Welcome to the Popular Plumbing, Kitchen, Bath Advice Site
  We're sponsored by:
Buy plumbing supplies online
www.PlumbingForum.com
THE Dynamic Plumbing, Kitchen and Bath, Information, Advice and Sharing Forum


Over 525,000 Posts in over 155k Threads

The most popular positive STRICTLY PLUMBING INFORMATION SHARING FORUM board on the Net. Ask any toilet, sink, faucet, pump, water quality and other plumbing related questions here. Plumbing professional and DIY tips, tricks, shortcuts, remodeling, plumbing advice forum and blog. Please refrain from asking business, pricing, contractor referrals, legal or any other non strictly plumbing related questions keeping all positive and with no advertising. 

New TopicSearchLog In Newest Messages
 hot water won't stay hot...again
Author: thornev (NY)

Well, my hot water problem is back again. I had the coil replaced, but it only provided marginal improvement. I get hot water right away and then it goes cold after about 1 minute. About 10 minutes after that, the water starts to get warm again but never as hot as it was when I first turned it on. And then after 10 minutes, it goes cold again.

A local hydronics engineer said that Utica boilers tend to "underfire" (whatever that means) and recommended setting the aquastat at 155 LOW, 160 HI with a DIFF of 10. No difference.

An HVAC guy and I stood by the boiler to see if the thing is firing on and off correctly (according to a temperature guage at the top of the boiler) and it appears that it does. The symptom seems to be that the hot water is just not getting through the coil as we could hold our hands on the hot water outlet pipe and it was not getting hot even though the boiler was on for a few minutes.

I'm very frustrated. Thanks for your help. thorne

PS - my previous posts on this subject are here:
www.plbg.com/forum/read.php?1,334509



Edited 2 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

If the boiler water is hot, assuming this is an immersion coil and not a side arm heater, then the water has to get hot unless it is flowing through the coil too quickly, or the coil's fins are obstructed.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

Other possibilities are.... a boiler tech down-sized the nozzle, because that's what he had on the truck,and it is under-firing.A tempering valve is wide open,or plumbed incorrectly.If there is a tempering valve, take a good look at it with a flashlight. It will probably be marked H,C and Mix.If they flip-flopped the hot and cold,you'll run straight cold water and meter small amounts of hot.



Edited 1 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Yes it is an immersion coil. I did try closing the cold water inlet valve (to reduce the cold water flow through the coil) to the point where the water pressure at the bathroom faucets is unacceptable. That helped a little but not enough. I should note that when I open all the way the "tempering" valve (not really a tempering valve - see last paragraph below), the hot water coming out of the coil is much better (because the cold water pressure going to the coil is reduced?), but then because there is more cold water being added in to the hot water, the water temperature at the faucets is colder than with the tempering valve closed.

I considered fin blockage so I had the installer check the old coil to see if there was blockage. There wasn't. SO we ruled out that sediment is blocking the heat transfer/water flow.

The nozzle size seems to be 1.10 which is what the hydronics engineer said it should be.

There is no tempering valve. It is a regular hose bib type valve and it is totally closed. Initially, as indicated in the post to which I refered, that was the problem. A tech had closed it to replace the coil gasket and then opened it all the way. After I closed it, it helped, but that fix didn't last long. thorne



Edited 4 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

It would have to be a boiler with a vastly undersized water chamber for the water running through the coil to cool it down that quickly, even if the burner did not fire immeditately, which it should not do in the first place.

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

It should be a tempering valve and turning the handle adjusts its setting so it adds or subtracts cold water from the flow. IF the water is hot to the valve and warm after it then it is the problem. If the water coming from the heat exchanger is warm, then it is the problem somehow, but we cannot tell how without being there.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

One thing that was mentioned by my HVAC guy is that, because the coil is at the top of the boiler, somehow the water level may not be getting high enough. But that makes no sense to me because then I'd have no hot water. But maybe it starts out high enough and then can't stay high? thorne

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

Not even a possibility unless you have a radiant system and all the piping is below the boiler. Open the safety valve and see whether air or water comes out.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

Start closing cold supply valves under sinks and vanities, one at a time, while running straight hot water at that fixture.Maybe you have a cross-connection problem.

Reply To This Message

 Re: hot water won't stay hot...again
Author: redwood (CT)

Your tempering valve should look something like this...

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Thanks for the tempering valve picture. That is definitely not what I have. Since I've got my valve completely closed, I assume that's not an issue.

I do not have a radiant system.

I have opened all the safety valves (there are 3) and only water comes out. I also bled about half the radiators to see if there is air in the system. Only water came out of the bleed valves so that's not a problem.

I'll try Paul48's suggestion when I get home tonight. That may be an interesting test because I had a cold water pipe leak last week and I turned off all the cold water supply to the upstairs bathroom (where the leaky pipe was) so I could fix the pipe. I also opened all the cold water valves in that bathroom to let air out. However, when I turned on the HOT water in the bathroom, water came out of the faucets where the cold water valves were open. That surprised me.

Thank you all for your feedback. thorne



Edited 2 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

I tried Paul48's suggestion of turning off the cold water feed to those faucets where hot water is a problem. No change. The problem is clearly isolated to the generation of hot water by the boiler.

What I did was a lot of experimenting in the boiler room. I turned knobs in different combinations and it seems the problem is partly that the cold water is flowing too quickly over the coil for the water to be heated, or that the boiler doesn't stay on long enough to keep the water running through the coil hot. I can't reduce the cold water flow anymore without making the hot water a trickle so I turned up the aquastat - LOW is now at 165 and HI is at 170. Hopefully that will work because I don't know what else to do. thorne

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

If you could post some pics,showing as much detail as possible,maybe someone here can come up with an answer.Set the Hi-limit at 170 and the Low-limit at 150. I think if you look at the front of the Aquastat it tells you to set the Hi at least 20 degrees higher than the low.What do the specs. for the tankless say it will produce as far as hot water?

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Paul48 - I know about the 20 degree difference. One guy who's working my case said he spoke to a hydronics engineer who recommended setting them 5 degrees apart (because he said Utica boilers tend to "underfire" whatever that means). That hasn't helped.

The main guy I'm working with now thinks that the aquastat is bad because the boiler doesn't fire on soon enough to heat the water. i.e. you can put your hand on the hot water outlet pipe and feel its getting cold before the boiler kicks on. But the 2nd symptom is that even after the boiler kicks on, the water through that pipe never seems to get hot enough which could indicate that the aquastat isn't reading the boiler temperature properly and therefore not STAYING on long enough. The only time the water is hot enough is when I first turn on the hot water.

I'm going to time exactly how long it takes for the boiler to kick in after I turn on the hot water. I'll report back here.

The aquastat is a Honeywell triple aquastat model L8124A-1130. I've read the manual on it many times, but there's nothing in it that helps me with this problem. I've tried changing the differential to 15 then 20 and raising it makes it a little worse.

What do you want to see in the pictures? thorne



Edited 2 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

What you should do is get a good plumber who knows how to analyze the situation and find out where the problem is. Just raising the water temperature is not a solution unless the coil is too small for the demand. The burner should not ignite until the water temperature in the boiler has dropped, and that should not happen instantaneously, or even quickly just from the water running through the coil, with any proper sized boiler.

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

You are checking the wrong symptoms. IF it is a boiler water temperature problem the pipes ON THE BOILER would get cool also, not just the water coming from the water heater coil. You need a plumber who can diagnose the problem, not one who is just guessing what could be happening.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

hj - I appreciate your input. I did get 2nd HVAC guy and his analysis was that it is the coil. But I had already replaced the coil and that did nothing. The odds that 2 coils are both bad is too slim, so my analysis is that it's something else.

My main guy just this morning told me when he put in the new coil that he noticed a crimp in the aquastat's oil-filled capillary. So now he thinks the aquastat needs to be replaced. At $165 (his cost for a new digital model) I guess it's worth a try since nothing else seems to be making a difference. thorne

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

OK........The DHW will work off the Hi-limit.A ten degree drop from that setting should fire the boiler.Why he has you changing the low-limit and differential settings to try to fix this problem,I haven't a clue.Those are the settings used to control the boiler and circulator pump on a call for heat only.Unless the boiler was a no-name boiler,built by hillbillies in a garage,it does not tend to under-fire.Boiler manufacturers go to great lengths to match burners,pressures and nozzle sizes to get the highest efficiency they can possibly get out of a boiler.If you set the Hi-limit at 170, does the boiler come up to that temp. and shut off?Did the installer provide a means of removing air from the top of the immersion well?Impossible to bleed without it.Sorry, but I have some doubts because of the gate valve used as the tempering valve.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

If the boiler works properly to the settings,like I said.Tell him to fan ice.At this point, pictures may reveal what has been done incorrectly with the install.



Edited 1 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Paul48 - The boiler does seem to fire at appropriate times, but the temp gauge at the top of the boiler always reads about 10 degrees higher than the aquastat settings. Note that I'm only talking about DHW, not heat. Until today I haven't turned on the heat.

My understanding is that the HI is the shutoff temp for the boiler when there's call for heat but not DHW. I thought it is the LO setting at which the boiler turns off for DHW. And with my aquastat model I thought it is the setting on the DIFF dial that causes the boiler to fire up for DHW (i.e. when the temp drops DIFF degrees below LO). Did I interpret the aquastat manual incorrectly?

There is a barrel-shaped relief valve at the top of the boiler that has a screw-on cap. I unscrewed it and hot water comes out, no air. There is one attached to a heat water pipe outlet too. No air from that one either.

The only reason I keep my main guy on the job is that he was the one who said I needed a new coil. Since that proved wrong and he charged me for the work anyway, I kinda feel like he needs to get it right if he can. At least he's being nice by sticking with it and not charging me for his time.

I'm still not sure what pictures would help you help me. Pics around the coil? The plumbing which is all over the boiler room?

Thanks for your help. thorne

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

I have a problem with anyone's diagnosis other than my own. The information you are giving us IS describing a coil problem of some kind. And the possibility that it is a boiler water problem is so remote as to be laughable. IS the boiler termperature dropping down to less than 115 degrees while this is going on? If the temperature is higher than the hot water setting, it is NOT a boiler, aquastat, burner, or anything else with the boiler.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

Look back in the postings...There is one misspelled Aqustats..I attempted to explain them there.Keep in mind there is no way the boiler knows there is a call for DHW other than temp. It is not a modulating gas boiler, therefore if the boiler is firing, it is producing as much hot water as it possibly can.It does know when there is a call for heat, and switches to the Low-limit and differential settings.And again, if the boiler was running on a call for heat, and you were running the hot water in a sink, it is producing as much hot water as it possibly could.As for the actual temp. readings varying a few degrees from the control settings, I wouldn't spend the money to change the Aquastat.I believe hj can help you with the other aspects of your problem.He seems to feel you have a problem with the new coil as well. Best Wishes:-)

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

hj - No, the temp never gets below 115. It ranges between about 10 degrees higher than where I have the aquastat's LO setting and then drops 10 degrees or so when the water cools down. I figured that the temp gauge reads higher than the aquastat setting because, well, the temp gauge is simply inaccurate or, because of where it's placed on top of the boiler, it simply is hotter up there with the steam and everything.

It's hard to swallow that the coil is the problem because I'm on my 2nd coil and they both exhibit the same problem. The odds that TWO coils are bad is slim but possible. Are there any tests I can do to prove one way or another if the coil is the problem? thorne

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Paul48 - I think you've got the aquastat behavior backwards. See here:

www.kerrheating.com/online_Training/HomeHeating/PDF/Tankless_Coils_&_Triple_Aquastats.PDF

thorne



Edited 1 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

thornev.....I'm looking at Honeywell's literature.I looked at the site, and they have it written exactly opposite of the way Honeywell( the manufacturer)says, and through watching,it actually works.I'll stand by what I said, it's your choice if you want to believe that web site.



Edited 1 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

I don't know how things have been plumbed in your case.I believe, and am guessing that you have pressure equalizing at the coil.Look at fig.6 on this site for typical piping. [www.smithboiler.com]

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Paul48 - I don't mean to be disrespectful or anything. I'm new at this and I do appreciate your help.

Pictures of my boiler:
[thornev.net]
[thornev.net]

boiler1.JPG shows the coil, aquastat, pipes, and temp and water pressure gauges. Cold is top pipe, hot on bottom. boiler2.JPG shows the pipe where the cold water gate valve feeds the DHW hot water pipe.

What's confusing is that the aquastat's LO and HI settings affect both DHW and heat operations. But there is a difference in the behavior when there is a call for heat and not. What I'm reading is that, with no call for heat, the burner ("RB") turns on when the water temp drops to LO-10 and stays on until the water temp reaches LO-10+DIFF. So for example if LO is set at 140 and DIFF at 10, the boiler turns on at 130 and turns off at 140.

When there *IS* a call for heat, the burner turns on at any water temp below HI-10 and turns off when the water temp reaches HI. For example given the same LO and DIFF settings above, if HI is set at 180 and there is a call for heat, the burner turns on at any water temp at 170 or below and turns off at 180. If there is no subsequent call for heat, then the burner reverts back to the LO and DIFF settings and won't turn on again until the water temp reaches 130.

To summarize, in terms of when the burner turns on and off, I assume that the behavior when there is a call for heat overrides the behavior when there is no call for heat i.e. for a call for heat, the water needs to be hotter than for DHW and the burner therefore stays on longer to reach the hotter temp.

Now am I reading this correctly? thorne



Edited 5 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

The Hi-limit has a preset and fixed "differential".It will fire the boiler, if the temp. drops 10 degrees below the Hi-limit setting.Bear in mind the boiler does not know there is a call for DHW ,other than the fact it sees a drop in temp., and at 10 degrees below Hi-limit, it will fire.The differential setting works in conjunction with the Low-limit setting only.Given the fact that the Aquastat is reading the boiler temp. in close proximity to the tankless coil, on a call for heat, if you were running hot water,the boiler would continue firing or not based on the low-limit settings, and the circulator would be on or off based on the differential setting.With no call for heat the boiler maintains the Hi-limit setting to provide additional hot water for a call for heat.You already know that to be the case,in a previous post, you stated it came up about 10 degrees higher than that setting.



Edited 2 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Paul48 - I'm obviously missing some basic boiler knowledge. I don't understand why there is a LO and DIFF if the burner is always going to turn on at HI-10. It seems to me that regardless of call for DHW or not, the boiler is going to keep the water within the HI and HI-10 range. Feel free to direct me to a web site that explains all this at a Boiler 101 level. I've looked around but found nothing.

Did the pictures in my previous post help? thorne

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

On a call for heat from the thermostat the boiler switches to Low and differential.Otherwise in a static state it will maintain itself at the Hi-limit temp.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Here's a new twist... The pressure relief valve keeps opening, letting out hot water. It's doing this every day that I take a shower or use large amounts of hot water (e.g. clothes washer). I have a 1/2 gal. bucket to catch the water and I've had to empty it for the last few days since I turned up the LO and HI on the aquastat. I turned the LO and HI down 10 degrees each so we'll see what that does. thorne

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

You are forgetting the heat transfer function. The hot water in the boiler, and it is hot regardless of whether the burner is running or not, is what is heating the hot water coil. The burner only fires when the coil has extracted enough heat from the stored water to lower its temperature. Therefore the burner has little to do with the temperature of the water leaving the coil, at least for a substantial period of time, assuming the stored water volume is not miniscule.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

Back up.........Are you getting hot water now?

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

Pictures of the piping into and out of the hot water coil along with that mysterious "valve" would help even more. The second picture does not tell us where the piping is going and therefore is just a nice picture of some pipes.

Reply To This Message

 Re: hot water won't stay hot...again
Author: hj (AZ)

In a hot water boiler there should not be any "steam and such" anywhere even at the top of the boiler. And definitely not below 212 degrees F, (actually higher than that because of the pressure factor). The outflowing water can NEVER be hotter than the boiler temperature, and because of inefficiencies in the transfer rate, the lower the boiler temperature relative to the volume flowing through the coil, THAT will affect the outlet temperature. Ideally the boiler would be at the normal operating temperature to produce the maximum amount of hot water, and then you would have a tempering valve to modulate it down to a usable/safe temperature.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

I agree..Wider angle pics of the piping in and out of the coil would be great. Someone has to have a clear understanding of how it has been plumbed,and I suspect there may be a mistake hidden by all that insulation.Let's back up a little....What was the previous source of hot water for the house?Any problem?Is the boiler newly installed?As for it discharging pressure...Shut the boiler down,close the supply valve to the auto fill regulator and carefully release pressure from the boiler down to about 10 p.s.i.,then open the supply valve.The pressure should only come back up to about 14 or 15 p.s.i..If it's higher than that the auto fill regulator needs to be adjusted.Wait a couple hours without running the boiler to make sure the pressure doesn't creep back up.Release a small amount of air from the expansion tank,if water comes out,it is ruptured and needs to be replaced.If not, fire the boiler and if the problem persists, you need to get a larger expansion tank.If you have a #30, get a #60.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Paul48 - No change since you came "back up".

The boiler was installed in 1999 and replaced a previous boiler about which I have no info (I'm the 2nd owner of the house which was built in 1960 and I bought it in 2005). I don't recall their being a hot water problem when I moved in (other than the boiler flooded my basement when I first turned on the heat - I think the boiler had been sitting idle for most of 2005.). The problem, to the best of my recollection, started when the coil gasket was replaced to fix a leak. At that time I believe the tech closed all the valves and when done, opened them all the way including the cold water gate valve that feeds into the hot water. When another tech closed the cold water valve feeding the hot water, that helped but led to the current problem.

My expansion tank rarely fills up with water and when it does, it's a very small amount. The size of the tank looks to be about 100-200 gallons.

I'll try the pressure release this weekend.

Do you think that I need to replace the gate valve with a tempered valve? The system was working with the gate valve so I can't see that replacing it would have an impact on this problem. Right now I have the gate valve completely closed because if I open it, the hot water gets colder faster and gets much colder.

hj - I believe the boiler water is heating correctly according to the way the aquastat is set, so then my problem has to be something with the coil. I think you said that early on, but how can a new coil go bad so quickly? I just wish I could prove it some other way because installing a 3rd coil means I have to try to get a refund on the 2nd coil. thorne



Edited 1 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: Paul48 (CT)

It's time to get a good plumber.......Forget the "engineers" and the HVAC guys.That install screams DIYer.You are going to damage the boiler.I suspect that gate valve is broken and not actually closing, but either way it needs to be straightened out and made right.No offense,but I'm talking about your expansion tank for the boiler, and your talking about your well tank.You're asking hj if the boiler water is DHW.We couldn't educate you fast enough to avoid damaging the boiler.Don't be penny wise, and dollar foolish.Best Wishes:-)

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

I just had a plumber here and he said it seems like a coil problem (or wrong coil model for my boiler or poorly-manufactured coil), but since the coil is new, he can't really blame the coil. He recommended installing an indirect and be done with the problem once and for all. Fine. I just need to win the lottery. =:-( thorne



Edited 2 times.

Reply To This Message

 Re: hot water won't stay hot...again
Author: LemonPlumber (FL)

Just be sure all the swing checks close.Good Luck.

Reply To This Message

 Re: hot water won't stay hot...again
Author: thornev (NY)

Well, after 4 plumbers and no one could fix the problem, I broke down and had an indirect fired water heater installed. After over a year, it is SOOO nice to have full pressure and long durations of hot water again! AHHHH! thorne

Reply To This Message


Note: Inappropriate messages or blatant advertising will be deleted. We cannot be held responsible for bad or inadequate advice.

Warning: Plbg.com has no control over external content that may be linked to from messages posted here. Please follow external links with caution.

Plbg.com is strictly for the exchange of plumbing related advice and NOT to ask about pricing/costs, nor where to find a product (try Google), nor how to operate or promote a business, nor for ethics (law) and the like questions.

Plbg.com is also not a place to ask radiant heating (try Heatinghelp.com), electrical or even general construction type questions. We are exclusively for plumbing questions.

Click here to view our old forum messages



to: Contact Us
to: Plumbing Manufacturers Address Directory
to: Plumbing Links Site
to: How to show an image
to: theplumber.com
to: Plbg Statistics
to: our FAQ's
to: Advisor List
to: Common Plumbing Terms
We're sponsored by:
Buy plumbing supplies online
  We're sponsored by:
Buy plumbing supplies online

Copyright© 2014 Plbg.com. All Rights Reserved.