Hi Guys... my boiler keeps shutting off even though the thermostat is calling for heat & the circulating pump is pumping... a plumber told me he thinks its the Aquastat Relay... anyone with any other ideas before I replace it?

here are pics of the system:

[www.flickr.com]

Thanks!

I forgot to mention one thing... if I flick the power switch off then back on, the boiler fires up... but eventually shuts again.

There is not enough information to determine what the problem is.

You need to check the various functions of the aquastat with a multimeter to see if that is the problem.

There are numerous things that can cause your heating system to behave the way you describe.

Your best option is to call a qualified heating technician to properly diagnose your problem.

Of course, if you want to start changing out parts, eventually you will fix the problem by process of elimination, maybe...

it should be pretty simple to find the problem. once it has failed, use a multimeter to see if there is 24V at the gas valve. that's a pretty old boiler so there probably isn't a spill switch or vent damper for the 24V to pass thru. 24V no doubt comes from the control straight to the gas valve.
ahhh the good old days. when trouble shooting was truly simple, easy to fix and cheap..
now, if it has failed and there is 24V present at the gas valve, then it is the gas valve itself.

Tommy...time for a new boiler.

The gas valve is not 24v, it's milivolt.

do you have wire schematic??can you jump the high limit?temporarily to see if it fires?belay that.can you post brand and model of boiler?



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i was looking at the photo of the operating control. it says 24V burner down in the lower left corner.

Try this website [forums.invision.net] or better yet, call another Plumber (that does heating work) instead of replacing parts that might be good.

e-plumber
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"The society which scorns excellence in Plumbing as a humble activity and tolerates shoddiness in philosophy because it is an
exalted activity will have neither good Plumbing nor good philosophy: neither its pipes nor its theories will hold water." -
John William Gardner 10/8/1912 - 2/16/2002

Repair your leaking Plumbing fixtures ASAP [www.theplumber.com]
This slow drip will waste 7+ gallons of water per day.

TRy jumping out the thermostat it could be defective,
JOCKO

You are correct Coach, in my haste to keep a short response, I should have explained it is not enough to check the 24v burner circuit, but the milivolt generator needs to be checked as well.

If either one of these sources fail, or are failing, the gas valve will not open.

Thanks for keeping me thinking.

The times I saw a millivolt generator or typical thermocouple fail, the pilot light would not stay lit.

e-plumber
-----------------------------------------------------------------------------------------------------------------------------------

"The society which scorns excellence in Plumbing as a humble activity and tolerates shoddiness in philosophy because it is an
exalted activity will have neither good Plumbing nor good philosophy: neither its pipes nor its theories will hold water." -
John William Gardner 10/8/1912 - 2/16/2002

Repair your leaking Plumbing fixtures ASAP [www.theplumber.com]
This slow drip will waste 7+ gallons of water per day.

That is indicative of a failed generator, however, milivolt generators will have varying outputs of power, in relation to the heat source.

It could be enough to hold the pilot open, but not enough to open the gas valve.

Given the original poster's problem, this scenario is unlikely anyway, but an interesting pusuit of discussion.

MV generators are 250 - 750 MV. 250 mv being the minimum required to hold the gas valve open, easily checked with a meter. If its low or borderline, it might be just that that pilot needs cleaned or the generator is failing itself.

Could also be the T-stat, burner relay, or the transformer dropping out under load. Unless you're good with a meter, you would probably be better off calling in a pro.

SOLVED!

Ok all you "rocket scientist"... (just joking), lol

let me teach you all something... when the system would shut off, the pump would still be on, when I turned the main switch off then on again, the boiler would turn on, but eventually go off again... I located the part & was ready to purchase it, but said to myself, "let me check the wiring in the main switch", so I opened it up & it looked fine, but as I was handling it, the boiler would go on & off, so I decided why dont I just repacle this $1 switch & see what happens... well guess what guys, that was it!

you guys owe me now... lol

That is why it is nearly impossible to diagnose electrical problems over the internet.

Like so many other threads on this site, it took on a life of it's own. I don't think we were discussing a concrete solution to your particular problem.

We just were persuing an interesting rabbit trail.

I confess I've wasted a lot of time looking for deep technical reasons for a problem, only to find a loose wire, or broken switch, Arrrggh!

Alot of things in life have very simple solutions,

yet we complicate them...



Now you can imagine all the people who get ripped off in this world!

Before you start patting yourself on the back, I would also consider remounting the electric wire harness going into the motor. I noticed that wires appear connected but not mounted and protected in the metal terminal box on the Bell & Gosset motor box. Or was that just me?

Best Wishes

where would th wiring sysmatic have started???

Wheelchair, yes, but the pump continuously ran, even when the boiler shut down, so those wires were not the issue here...





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