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Discuss Problems with shower mixer valve in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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I removed a bath from my sister in law’s bathroom about eight years ago. I cut back the hot and cold to the bath and branched off these to a new shower bar mixer. It worked fine until about two years ago when I fitted a new valve which has been fine until about two weeks ago when she said it wouldn’t maintain temperature and was sometimes running cold. I doubted that the valve would have gone so quickly in a one person household so I took a brand new Grohe valve that I had to test it and sure enough this didn’t solve the problem. I then ran the wash hand basin tap and this also would not maintain temperature so clearly not the shower valve. The kitchen tap was absolutely fine and ran consistently hot. She has a maintenance contract with British Gas on the boiler so I suggested she try them. The engineer came and said the heat exchanger needed replacing( I doubted if this was the problem because the kitchen tap was absolutely fine but I thought they should know better than me) He has been replaced the heat exchanger and it is no different. He said it is a plumbing problem and thinks there must be water passing somewhere? Why would it work Ok for eight years. The house has low water pressure but then it always has had.
Any advice would be much appreciated.
 
What type of valve did you fit 2 years ago and why.
Can you measure the wash hand basin flowrate by monitoring the exact time it takes in seconds to fill a 1 litre container and do likewise with the hot kitchen tap.
 
What type of valve did you fit 2 years ago and why.
Can you measure the wash hand basin flowrate by monitoring the exact time it takes in seconds to fill a 1 litre container and do likewise with the hot kitchen tap.
It’s just a shower bar mixer valve not a separate valve.Yes I could measure the flow rates but the wash hand basin has always been much slower than the kitchen. As I said the house has low water pressure and it has always been much worse upstairs than down
 
The boiler has a flow switch which shuts down the burner at a ~ 2.5LPM, this may be faulty, if the wash hand basin is anything > than say 3LPM then switch probably faulty, I would suggest then open the kitched tap slowly until you just get hot water, then measure this.
 
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The boiler has a flow switch which shuts down the burner at a ~ 2.5LPM, this may be faulty, if the wash hand basin is anything > than say 3LPM then switch probably faulty, I would suggest then open the kitched tap slowly until you just get hot water, then measure this.
This is now sorted. Sister in law had contract on boiler with British Gas, first engineer said it needed a new heat exchanger which I knew it didn’t as kitchen tap worked fine. Her boiler then stopped working completely, second engineer said it had a blocked fan and Venturi since being cleared both boiler and shower have worked fine.
 

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