Water in Mixer Shower from Combi Keeps Going Hot/Cold

Leodogger

We live in a bungalow and have a mixer shower in the bathroom that is situated next door to the Vaillant Eco Max Combi Boiler. Since we moved in we have not been able to have a shower without dodging in and out of the spray due to it going very hot for a few seconds and then cold, then hot again and so on. We have tried adjusting the pressure spray and heat controls but nothing changes the hot/cold problem. We also have to wait ages to get hot water to our kitchen hot tap which is about 15 ft away (in pipe terms) from the boiler. This problem seems to be more or less the same when the central heating is on too.

Is it a matter of a faulty pressure valve, or as a local plumber said when he was here doing another job, that it might be the thermal plate which is corroded up and needs cleaning (he suggested taking it out annd putting it in a container of Coke ???? which he says will take the rust off anything!).

Anyone have any ideas what might be causing the problem? We don't know the age of the shower but it could be as much as 7 or 8 yrs old and is a Frederick Grohe.

bridgedino

Very possibly a faulty thermostat within the shower.

If the hot taps elsewhere work fine then you can then be 99% sure that its a shower fault rather than a boiler issue

EssexExile

bridgedino wrote: »

Very possibly a faulty thermostat within the shower

If it's a thermostatic mixer.

Leodogger

EssexExile wrote: »

If it's a thermostatic mixer.

How can you tell if it's a thermostatic shower? It has a lever handle on a bar below the riser rail which goes left for hot and cold for right and goes up and down to control the pressure of the water spray but other than that I don't know how to tell, I am a mere woman

AVERAGEJOE_2

Usually mixer shower will be of thermostatic type they have cartridges inside that need replacing every now and then just put make and model into the web and see what parts come up usually around £50.

Does kitchen tap stay hot ? and is it just that tap

spannerzone

My thermostically controlled Bristan shower mixer went faulty after only 18 months and did odd hot/cold problems and wouldn't get hot enough. I got a new thermostic cartridge from Shower doctor (the cheapest at the time) and it's been find since. The plastic crappy looking cartridge didn't look like it would last long and the orignal didn't.

The hardest part was determining the exact part required as there's so many. Fitting was remarkably straighforward.

WillowCat

JWhite wrote: »

How can you tell if it's a thermostatic shower? It has a lever handle on a bar below the riser rail which goes left for hot and cold for right and goes up and down to control the pressure of the water spray but other than that I don't know how to tell, I am a mere woman

From that description it sounds like a mixer shower rather than a thermostatic shower.

I have one of those; my plumber warned me of the problems you are having, but I had him fit a pressure equalising valve, and it works just fine with our combi boiler. If you can gain access to the pipework then you could retro fit one.

For example: http://www.plumbworld.co.uk/pressure-equalising-valve-344-20563

Leodogger

AVERAGEJOE wrote: »

Usually mixer shower will be of thermostatic type they have cartridges inside that need replacing every now and then just put make and model into the web and see what parts come up usually around £50.

Does kitchen tap stay hot ? and is it just that tap

My husband says the kitchen tap stays hot once the hot water comes through. All I can see on the shower is that it is a Frederick Grohe shower but no model no. shown anywhere.

Any place I can look for it ?

Leodogger

WillowCat wrote: »

From that description it sounds like a mixer shower rather than a thermostatic shower.

I have one of those; my plumber warned me of the problems you are having, but I had him fit a pressure equalising valve, and it works just fine with our combi boiler. If you can gain access to the pipework then you could retro fit one.

For example: http://www.plumbworld.co.uk/pressure-equalising-valve-344-20563

Just taken a look at this part and it looks the job but I am wondering if it is compatible in a bungalow where we don't have gravity feed. If I can ensure it will not affect the pressure to the shower head adversely, it may be what we are looking for Also I don't know what our water pressure (PSi) is.

WillowCat

I've had two, first was in a bungalow with a megaflo (mains pressure hot water) cylinder, the second in a house with a combi boiler.

I don't know about flow restriction as they were fitted from the outset so nothing to compare them with. Yes, the flow reduces if someone, for example, flushes a loo, but the temperature remains constant.