Unusual hot water problem-one for debate!

[zanwan]

Hi

I've been asked to go out to have a look at a hot water issue at a house, where the hot water in the bath and bathroom basin constantly changes from hot to cold, so it will be hot for 20 seconds, then cold for 20 seconds.

Now the unusual thing is the hot water in the kitchen, and in the upstairs toilet is fine, its constantly hot.

The setup of the house and boilet is like this.

Boiler is in kitchen. The upstairs hot water goes straight up from the boiler. Then after the boiler you have the kitchen. Hot water here is all fine upto this point. Then you have the bathroom. Hot water in bathroom keeps changing from hot to cold. Both bath and basin taps affected.

Now if it was ALL the hot water taps in the house, i would assume its the plate heat exchanger. But because some taps are ok, my only guess its either something to do with the pressure or something to do with the hot water pipework as it goes into the bathroom.

Anyone ever come across anything like this before? I'm totally lost as to what could be causing this!

 

[bengasman]

Ariston by any chance?

 

[zanwan]

Nope, its an Alpha boiler

 

[tonybhoy]

Probably a faulty shower mixer or bath mixer

 

[bengasman]

Would still suspect the hex.

 

[zanwan]

but wouldnt the hex affect the hot water to all taps?

why would it affect just the downstairs bathroom?

Could a blockage in the pipes not cause this?

 

[kevplumb]

but wouldnt the hex affect the hot water to all taps?

why would it affect just the downstairs bathroom?

Could a blockage in the pipes not cause this?

check the flowrate upstairs and down

 

[zanwan]

flow rate is fine on all taps, kitchen, bath, basin, and upstairs basin. no difference in any of these.

 

[tonybhoy]

It's not the boiler otherwise all of the taps would be the same, pound to a penny it's a dodgy basin mixer, bath mixer or shower mixer.

Cold water will be going back into the hot via one of those and causing your problem. You'll have to start isolating all of those in order to pin the problem down.

 

[zanwan]

The bath taps are mixer taps, normal mixer (not shower mixer).

The basin tap are single taps, and the hot water on this, and on the mixer tap are the same, i.e. goes hot then cold then hot again....

My assumption is the pipework, but i'm not very experienced so not sure if a blocked pipe could cause this.

 

[kevplumb]

if it was a blocked / partially blocked pipe the flowrate would be reduced

 

[zanwan]

you see thats the weird thing about this, the flow rate is fine on all taps. So that rules out a blocked pipe.

(scratching head)[/img]

 

[picasso]

could be a worn diaphragm, I am assuming its a combi

 

[zanwan]

Its an Alpha combi

 

[powell30]

Re-read what has been posted.....the clue is MIXER........one of em is letting by. That means cold is pushing into the hot line affecting the closest hw draw offs. Try isolating each cold min turn on the mixer taps and recheck