Hot water issue which has me baffled

[Paul Cockhill]

I would really like some advice about a problem with a hot water issue. I am a registered plumber and fitted all the heating pipes and hot and cold water pipework for my sisters house back in 2012. I also fitted a Megaflow unvented heating cylinder. Everything has worked really well until last week where she is having issues with her hot water. Her shower works fine and supplies good hot water, however she is not getting any hot water in her kitchen tap, or she has to run the water for at least 2 minutes until she gets some hot water from that tap. Then the water temperature varies and comes and goes.

I went to the property last Friday and could get hot water from the bath hot tap and the washbasin hot tap, also in the bathroom. I was also getting hot water in the downstairs bathroom washbasin tap but could not get any hot water from the kitchen hot tap.

The only taps or valves which have thermostats is the shower, which is working fine.

I have checked the megaflow and that is working fine and the pipework going out of the megaflow feels hot. The megaflow is on the 1st floor and next door to the upstairs bathroom. The kitchen is on the ground floor and the downstairs bathroom is next to the kitchen.
The kitchen tap is almost directly below the megaflow.

I just cannot understand what has caused this problem.

Does anyone have any suggestions on something I might have missed

Many thanks

Paul Cockhill

 

[Basher]

Is the kitchen tap a monobloc mixer?
Presumably the kitchen cold is fed directly from mains?
Is there a NRV on the kitchen hot?

Can you isolate the cold (only) at the kitchen tap, and/or same on the shower mixer?

 

[Paul Cockhill]

Is the kitchen tap a monobloc mixer?
Presumably the kitchen cold is fed directly from mains?
Is there a NRV on the kitchen hot?

Can you isolate the cold (only) at the kitchen tap, and/or same on the shower mixer?

Hi Basher, thanks for the reply.
Yes it is a monoblock mixer but I turned off the cold supply and just ran the hot through it but is was still just cold coming through
Yes the kitchen cold is coming from the mains
The is no NRV on kitchen hot

I can isolate the cold to kitchen tap but not on the mixer shower

 

[Basher]

Hi Basher, thanks for the reply.
Yes it is a monoblock mixer but I turned off the cold supply and just ran the hot through it but is was still just cold coming through
Yes the kitchen cold is coming from the mains
The is no NRV on kitchen hot

I can isolate the cold to kitchen tap but not on the mixer shower

Thanks Paul
Well that's shot down my theory!

I have a kitchen monobloc which doesn't take h&c separately to the spout, but mixes them directly after the valve/cartridge. I'm ashamed to say there's no NRV on the hot (yet), and if I turn both hot and cold full on, cold goes back up the hot into the cylinder etc. (So next time you don't get hot water for ages!) I had wondered if you had a faulty cartridge there might be something similar going on, but you've tried with the cold supply isolated, so not that ☹️

I also wondered if something similar might be going on at the thermostatic shower.
If that's fed from balanced cold, can you turn off balanced cold somewhere so as not to affect hot, and see if the problem still persists?

 

[Chuck]

The fact that the shower is delivering hot water does not rule out the possibility that it is not isolating the hot and cold feeds.

For a simple no-dismantling check: Run the shower so that its DHW feed hot to the touch. Keep your thumb on the shower feed and get someone to run the problematic kitchen tap. If the shower is passing your thumb will get cold rapidly as soon as the kitchen tap is run.

I'd take the opportunity to fit NRVs to the shower.

 

[Paul Cockhill]

Thanks Paul
Well that's shot down my theory!

I have a kitchen monobloc which doesn't take h&c separately to the spout, but mixes them directly after the valve/cartridge. I'm ashamed to say there's no NRV on the hot (yet), and if I turn both hot and cold full on, cold goes back up the hot into the cylinder etc. (So next time you don't get hot water for ages!) I had wondered if you had a faulty cartridge there might be something similar going on, but you've tried with the cold supply isolated, so not that ☹️

I also wondered if something similar might be going on at the thermostatic shower.
If that's fed from balanced cold, can you turn off balanced cold somewhere so as not to affect hot, and see if the problem still persists?

Hi Basher

There could be something in this. The kitchen tap is the first mains cold water feed after the stopcock. So could the cold be going up through the tap and pushing it way up the hot pipe, so when the hot tap is turned on it just pushes out the cold water? Perhaps if I put a NRV on the hot tap this might sort it??? A long shot but what do you think

Paul

 

[Paul Cockhill]

The fact that the shower is delivering hot water does not rule out the possibility that it is not isolating the hot and cold feeds.

For a simple no-dismantling check: Run the shower so that its DHW feed hot to the touch. Keep your thumb on the shower feed and get someone to run the problematic kitchen tap. If the shower is passing your thumb will get cold rapidly as soon as the kitchen tap is run.

I'd take the opportunity to fit NRVs to the shower.

Thanks Chuck, will try that

Paul

 

[Basher]

Thanks Chuck, will try that

Paul

I'm with Chuck, it may be the shower passing. Have seen posts about this sort of thing here before!