New Bathroom Hot Water Temperature Fluxuation

[faz54]

Since my bathroom refit I have hot water temperature fluxuation(runs stone cold for about 20 seconds) in both my bathroom Mira Excel shower and my bathroom basin mixer both are new and my bathroom sits above my Vokera boiler. My ground floor hot water seems unaffected.
Thinking it was a boiler problem I had British Gas out today and the engineer changed a sensor on the boiler but the problem still persists.

Any help would be appreciated.

Thanks

 

[BillyLiar]

Are you registered with British Gas for there boiler care service? If so push the matter, you are paying for a service and if there is a problem then I'd make sure they know about it.

 

[faz54]

I'm thinking that maybe the problem could be with the new plumbing and not the boiler as the downstairs hot water seems to run fine..This is not a mixer.
And yes I have BG service care.

Hi Guys
Could the basin mixer be faulty allowing the cold water to enter the hot water pipes.

I isolated the cold water to the basin mixer via the service point and all seemed good with the shower. As soon as I allowed the cold to enter the basin mixer the shower ran cold.

Does this mixer being faulty sound feasible?

The basin mixer is an Ideal Standard Cone Mono basin mixer

 

[heinz57]

It sounds to me as though the cold water pressure is forcing itself
into the hot water supply pipes as they are at a lower pressure. Get
two single check valves and place one on the sink cold supply and the other one on the shower cold supply. This should stop the problem, ask at
your local Plumbing merchants for right tools etc, save you making a second trip!

 

[bgec]

Try a pressure reducing valve on the cold as it enters the bathroom that way you can balance the pressure

 

[faz54]

It sounds to me as though the cold water pressure is forcing itself
into the hot water supply pipes as they are at a lower pressure. Get
two single check valves and place one on the sink cold supply and the other one on the shower cold supply. This should stop the problem, ask at
your local Plumbing merchants for right tools etc, save you making a second trip!

Unfortunately I'm unable to access the shower cold supply pipe

Try a pressure reducing valve on the cold as it enters the bathroom that way you can balance the pressure

Would reducing the cold flow to the basin mixer via the existing service valve have the same effect?

Thanks guys.