Mixer valve letting cold water into hot water feed

[elthorne]

Hi - just posting to see if anyone's had a similar problem to this:

I've been having intermittent problems with my hot water temperature going from hot to luke warm - not just in the shower but in sinks around the house. Over a two year period and many call outs I've had a new heat exchanger fitted in the boiler and a limescale inhibitor on the mains water inlet. A brilliant British Gas engineer came round today to fit a new heat exchanger. As he went to install it he isolated the hot water feed in the boiler and to his surprise cold water came out of all the hot water taps in the house. He said this was caused by a faulty mixer valve that was letting mains water enter the hot water feed and was probably caused by grit getting underneath a diaphragm in one of the mixers. By a process of elimination he identified the faulty valve as the one that operates my bath and shower (just my luck that it's the most expensive one to replace and concealed behind the bathroom tiles!)

Does anyone have any advice to offer on how easy it would be to repair the valve/diaphragm or should I just buy a new unit? At £300-£400 they seem a bit expensive and this faulty valve is only 4 years old.

Grateful for any advice. Thanks.

 

[seco services]

what make/model mixer is it ?

 

[elthorne]

It's a Crosswater KU2001C. The model seems to be long gone and there's little if anything I can find about it on Google. Looking at a technical diagram of the valve I can't quite understand how it's possible for the mains supply to feed the hot water system.

 

[Nige F]

Combi boiler a simple check valve on the hot feed to mixer should do the job or am I being too simplistic

 

[elthorne]

Nige - yes it's a Vaillant combi boiler. What's a check valve? Is it a sort of one-way restrictor?

 

[seco services]

yes as nige said use a couple of check valves on the feeds.
yes they are one way valves.

 

[elthorne]

Thanks both. Just to clarify - I can see how a check valve on the hot feed will stop cold water getting into the hot water system for the rest of the house, but am I right in thinking that it won't mend the valve problem and that the shower temperature will still be luke warm?

 

[banhamd]

Hi mate i have the same issue - also a cross water shower valve and a vaillent boiler. Spooky.

If you have a moment to tell me how your situation was fixed & how much it cost it would help me a lot.

regards,

Dan

 

[hi1]

At the moment the cold water is at a higher pressure than the hot water, when the shower is used the cold water pushes and or restricts the flow of the hot water to the extent of entering the hot water pipes this causes the hot water temperature to be lowered. A check valve would allow the hot water to travel up the pipe to the shower and stop the cold water affecting the shower temperature. If the cold water is still preventing the hot water getting to the shower there is a valve that can be fitted that you can regulate the cold water pressure with, possibly by trial and error without affecting the flow at the shower to much.

 

[elthorne]

Banhamd - after taking this one up with the mixer manufacturer back in February they suggested that I remove the thermostat cylinder and soak it in vinegar overnight as they thought the problem was most likely caused by a build-up of limescale.

And you know what? They were right! I've only had the problem once since then and it was solved (exactly as they suggested) by turning the shower on and off quickly several times which dislodged the limescale. Obviously a restrictor valve is preferable assuming you can get to the pipework, otherwise I'd (a) invest in a 50p bottle of malt vinegar and (b) get a schematic showing how to remove the thermostat cylinder. Hope that helps.

 

[banhamd]

thanks for the response,

I thought i'd better flesh it out a bit more to be sure of the issue;

When i installed the valve it was fine for a couple of years. Then we started to notice the hot water was luke warm and fluctuating from warm to cooler almost in the same cycle all the time.

It might be unrelated but at this time the entire water mains for this area was dug up and replaced with new plastic pipes. I am assuming less leaks and higher pressure as a result.

Went though the boiler engineer root and paid loads to have heat exchanger done etc. Seemed ok for a couple of weeks and then started up again, Engineer came back and we noticed cold water in the hot water pipes this time. We found with the shower turned off set to the cold position the hot water taps ran hot again. I could live with that as a solution.

However the situation has got worse and the only way now to get a hot bath is to actually run the cold water through the shower. I assume it diverts it away from the hot pipes or lowers the pressure so it doesn't go there...

the more I think about it the more i suspect something to do with the mains pressure increasing when they re-laid the mains pipes. It seems like too much of a coincidence. We did try restricting the flow to the boiler initially when we thought it was the boiler playing up by half closing off the stop cock. But it had no effect.

I want to avoid smashing down the rear wall of my shiny new shower with floor to ceiling porcelain tiles if possible - where would one have to fit the check valve? I am assuming close to the shower valve so you know you have isolated the issue. All help welcomed!!!

 

[banhamd]

thanks for that elthorne.. that sounds very plausible give amount of limescale here in Barking. perhaps the water mains work ( see my last response..) is a red herring after all!!

Will try it. Thank god it doesn't involve rippout out back of shower - took me 4 years to get round to putting it up

 

[elthorne]

We had a similar experience with British Gas - over an 18 month period they fitted an electro-magnetic limescale inhibitor (still not sure it makes any difference), flushed our system and replaced the heat exchanger (the engineer noted that the old one wasn't in bad nick but seemed confident it was the source of the problem). The fourth engineer suggested we install a sort of in-line sludge remover and it was only on the fifth visit when the problem was correctly diagnosed as the shower mixer. Good luck.

 

[Tori21]

Hi,
I found this thread, while trying to work out what the problem with my water system is & I'm wondering if anyone could advise me?
I live in a ground floor flat & have an old boiler & a mixer shower that has worked for probably about 7 years since I put it in. Since Christmas, there has been water coming from the header tank overflow. It's been intermittently & wasn't too heavy to begin with. But recently has been going for about 3 days & has been pouring a lot of water into the garden.
We've changed the ball valve in the header tank & this didn't stop the water. So I've had British Gas investigating, but the first engineer said that it was due to the system needing power flushed. So I've had that done (& will have to pay for the pleasure), the engineer who did that work looked into the problem after saying the power flush wouldn't help.
He has checked over the boiler, tank etc & thinks the only thing it could be is the mixer shower. Is it possible that the mixer shower could force water up 3 floors into the header tank & cause it to overflow?

 

[HERTS P&D]

New hot water cylinder is needed.

What the **** was a power flush going to do???


Andy