hot water coming through cold taps

[askjim]

Hi

I really hope you can help me.

I moved house a month ago and noticed hot water coming through the cold taps. Not isolated to a single cold tap but both cold taps upstairs and most likely both cold taps downstairs. The hot water will last for 15-20 seconds.

At first I was not too bothered but as we have a home care agreement I thought lets get this fixed and also because I think we had the same problem in the previous house which had the same boiler and was installed by the same guys but which we had previously put down to the cold and hot pipes being close together.

Please see first image

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• askjim
• 28 Oct 2013
• 1

Cold in comes into the bottom of the manifold and cold goes back out on the left of the manifold, the pipe on the left above the cold out is pressure relief / expansion tank and at top is the blender where cold comes in at the bottom, hot at the top and hot going out on the left.

The gas engineer put a device on the cold out and recorded the temp of the pipe at 45+ when the hot water was heating. After you have bled the cold tap and it goes from cold to very hot it then goes cold. If you leave the cold for 2 mins and then draw further cold it is hot and if left for longer would be very hot.

He spoke to ideal and they suggested switching the blender. I think he was told to do this because the non return valve was likely to be broken.

The blender was replaced and the problem remained. I don't actually think there is a non return valve in the blender.

The engineer spoke to his boss and they decided to replace both blender and manifold in case the manifold had a non return valve. Both parts were replaced and it was noted that the manifold contains a non return valve on the cold in. Still the problem remained.

So ideal came out to take a look who were perplexed and he rang his boss who suggested that the cold out was designed for a shower and that the hot out should have a non return valve inserted to fix the problem.

Instead the cold out was re-routed so it comes off the cold in but below the non return valve in the manifold - this assumes there is a non return valve - I did not get to see the manifold. See photo 2

But still the problem exists although I do not think the hot water in the cold is at hot. Weirdly when my wife ran the downstairs cold tap when cooking tonight the cold out seemed to go very hot (but I would need to check this)

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• askjim
• 28 Oct 2013
• 2

Please help as I would like to figure this out and especially as there is likely to be 35+ other houses where I live with this problem and as I would like to let the engineer know what the problem was.

A reward is offered for a correct diagnosis

Thanks in advance

James

 

[picasso]

If there is a nrv in the manifold and its working I would think the problem lies elsewhere, nrv in your showers or mixer taps or badly plumbed in washing machine perhaps, try isolating one thing at a time and see if the problem persists.

 

[Agile]

Where abouts are you?

 

[askjim]

Thanks Picasso.

I did not see the NRV in the manifold, is there a definitive test without having to remove the manifold?

Bit of a non diy'er. Would that involve removing the mixer shower and fitting blanking plates? Then see if that fixes the problem and if not try the kitchen tap?

Thanks

James

 

[picasso]

Without a nrv the heated water will expand down the cold so turn off the power to the hot water and run off until it runs lukewarm, turn power back on and feel the cold inlet to see if it starts to heat up,

without a nrv the cold pipe will get as hot as the hot water pipes, with a nrv the pipe may get slightly warm, might be a good idea to get the expansion vessel checked as well.

 

[askjim]

Where abouts are you?

Witney near Oxford.

 

[askjim]

Without a nrv the heated water will expand down the cold so turn off the power to the hot water and run off until it runs lukewarm, turn power back on and feel the cold inlet to see if it starts to heat up,

without a nrv the cold pipe will get as hot as the hot water pipes, with a nrv the pipe may get slightly warm, might be a good idea to get the expansion vessel checked as well.

Prior to the modification the cold out pipe was getting very hot and I think the cold in was slightly warm. It is not something I can definitely recall checking the temperature of.

Since the modification the cold in is slightly warm but no where near as hot as the manifold which is too hot to hold for any length of time.

The manifold was replaced prior to the modification.

As mentioned in my post I noticed that when my wife ran the downstairs kitchen cold tap the cold in went mega hot. I checked this, this morning and is definitely happening.

I have someone looking at the expansion vessel next Monday and will report findings.

Thanks for your input so far. If your diagnosis is correct I will be sending something in your direction.