Hi all, i've read some similar situations on the site but want to make sure given my situation. Our master ensuite shower will start of at a nice hot temperature and after about 5 mins will cool down to just warm. The shower temp at its coldest is tolerable, not freezing by any means but far from hot when we start. Leaving it off for a few mins will get us hot water again but short lived.

Hot water at the sink and throughout the house remains hot, much hotter than the shower so I don't believe the main mixing valve or the heat source (boiler) is to blame and am focused on the shower valve.

It is this hansgrohe thermostatic valve (and separate matching on/off valves for the water flow)
[spares.hansgrohe.com]

I've opened it up and cleaned out the cartridge, it wasn't in terrible shape but there was definitely some black debris caught in the screen. I tried out the shower and although I think it may have stayed hot longer, it eventually got cooler. When I moved the temperature valve past the safety stop direction to the maximum hot side the water did not get any hotter.

So I'm left with two theories or parts to replace:
1. Replace the thermostatic cartridge
2. Go further in my disassembly and look at the check valves to see if debris has gotten in there causing the mix to be off. In the diagram linked above these are the non return flow valves DW 16.

Am I on the right track with the above? Would you try anything else for diagnoses? Anything else I should look for?

One other question - should I grease the gaskets after cleaning and should I soak in a water/vinegar solution to remove calcification? We have had to recently replace our water softener because the previous one stopped working so there would have been a lot of time without softened water flowing through that shower.

Thank you for any help/advice.

bhaver

what you are saying is that once the shower runs cooler (5 minutes) if you turn on a hot faucet elsewhere it is still nice and hot?

Yeah that's right, the shower cools down but the rest of the house's hot water is fine, leading me to believe the problem is at the shower not the hot water source itself (boiler/mixing valve).

Likely calcium in the valve. Vinegar and water 1/2 and 1/2 soak should clear up the calcium. If you have screens to filter, soak those too.

srloren

You mean the thermostatic cartridge/valve or the check valves or both?

Thanks!

I would replace the thermostatic cartridge and the check/screens. If you're already that deep into the faucet, it would'nt make sense to not do a complete rebuild. Just my opinion. It'll save you grief when the checks go bad. Then you have to spend time diagnosing that.