Hot and then cold shower; faulty thermostatic valve?

Teh_Next · 22 Apr 2019 at 10:55

Hi,
I have a shower that runs from a combi boiler. It more often than not turns cold and is a real pain in the backside.
The shower is only 6 months old and it held a steady temperature at first but recently it's started turning cold...stays cold for a bit, heats up, turns cold....on and on. It's even turned itself off a few times.

I thought it maybe that the thermostatic valve was kicking in too aggressively as the warmer weather means that the shower receives hotter water, so I turned the water temp down on the boiler itself but it made no difference.

Really starting to tear my hair out now. It's a having an impact as it means a quick shower in the morning before work turns into a stand there like a plum waiting on the shower to go hot again and stay hot long enough farce! I'm having to get up a good bit earlier.

Any suggestions anyone?

gEd · 22 Apr 2019 at 11:35

I had a situation where the shower started hot and then after 5 mins, went cold. It proved to be a failing pump in the boiler.

chroniclard · 22 Apr 2019 at 11:49

Had this before, plumber descaled the heat exchange thing, working perfectly now. (Until it scales up again, hard water area, need to get a water softener)

Kol · 22 Apr 2019 at 11:56

Dumb question, but have you ruled the boiler out itself ie running a hot tap for a while to check whether it remains hot for the entire time?

Teh_Next · 22 Apr 2019 at 11:59

Kol said:
Dumb question, but have you ruled the boiler out itself ie running a hot tap for a while to check whether it remains hot for the entire time?

I have yes. All Taps run and maintain a consistent heat, even when using the mixer taps in the kitchen and bathroom.
So I think the boiler is (hopefully) ok.

NoobCannon · 22 Apr 2019 at 12:14

Sounds like the thermostatic valve to me.

Google your model number and see if you can find a replacement part

famas · 22 Apr 2019 at 12:24

Had the same thing with my shower, I took out the thermostatic valve and gave it a really good clean through as it was full of crud. I was expecting it to need replacing but I put it back in and its been fine since.

It's worth checking any filters on the tap connectors as they get gummed up to

Teh_Next · 26 Apr 2019 at 08:02

Well I managed to have a shower last night with no fluctuation.
I wouldn't tempt fate saying it's fixed just yet but, it's a start.

Basically I had to "reboot" the showers control unit. It's a digital shower. I had to turn off power to the spur the unit is wired in to. I had tried tripping the whole electricity but that apparently makes the unit just save it's settings as it thinks there's a power cut.
So one reboot later and we shall see how it goes.

gEd · 26 Apr 2019 at 23:51

well if it's a digital shower, that explains it. It's a binary system so basically either hot or cold.

Sin_Chase · 27 Apr 2019 at 01:24

gEd said:
well if it's a digital shower, that explains it. It's a binary system so basically either hot or cold.

Uhm... Surely a digital shower is still thermostatic. The set temperature is just controlled digitally instead of an analogue dial.

Magic_x_uk · 28 Apr 2019 at 09:29

exactly the same here recently.

CH working fine and hot. All hot taps working hot.

Triton HP Shower from combi boiler. going hot and cold. At times not even turning boiler on when demanding hot water.

Changed thermostatic cartridge on shower £114. Spot on now.

Musty Pie · 29 Apr 2019 at 13:04

Check the filters on the inlets to the mixer too! Sometimes they can chalk up.

Or as others have said new cart time!