Shower suddenly hot when downstairs toilet flushes

[kofi2003uk]

Mrs might have something to say about toilet filling slowly but hey I will just sleep in the shed when it comes to it LOL

 

[JohnD]

Next time you have some plumbing done, remember not to have the pipes hidden.

 

[Hugh Jaleak]

Supplies need to be balanced and dedicated to the shower. If you are correct and have an unvented cylinder, then I'd have expected any draw on the cold supply should be affecting the hot and cold supplies equally.

Not something we can easily diagnose from available information, really needs pipework tracing to see what's fed from where and further investigation as to why the cold supply is being strangled but not the hot.

Normally this happens with unbalanced supplies, Hot fed from a Vented tank, and cold from the mains, as hot supply remains steady from the stored supply whereas a draw on the cold supply lowers available cold supply to shower with the result, shower user is scalded....

 

[kofi2003uk]

thank you. although this property was only build in 1999, the pipe layout isn't the best. i will have to use one of 2 options, it seems

1- reduce the flow on the downstairs toilet as advised above or
2- get a new shower with thermostatic control to regulate the water temperature for the shower.

i will talk to my plumber about it. thank you all for the advice and comments. its appreciated.

 

[Agile]

In theory you should already have an ISO valve fitted on the water inlet to the toilet cystern.

It should be turned to reduce the flow rate to about 1 li/min.

 

[Harry Bloomfield]

Supplies need to be balanced and dedicated to the shower. If you are correct and have an unvented cylinder, then I'd have expected any draw on the cold supply should be affecting the hot and cold supplies equally.

Precisely, and I'm guessing his shower is a simple mixer shower, rather than a temperature controlled mixer.

 

[kofi2003uk]

thanks chaps

 

[fixitflav]

Precisely, and I'm guessing his shower is a simple mixer shower, rather than a temperature controlled mixer.

Quite. That's the obvious answer.
The shower looks very fancy so I'd have thought it would be thermostatic, might be worth studying the manual and perhaps speaking to the maker to check whether it should be. If so maybe the cartridge has failed and can be replaced.

 

[Harry Bloomfield]

Quite. That's the obvious answer.
The shower looks very fancy so I'd have thought it would be thermostatic, might be worth studying the manual and perhaps speaking to the maker to check whether it should be. If so maybe the cartridge has failed and can be replaced.

I agree, but it still doesn't explain why there seems to be a difference in flow, or pressure, between the hot and cold.

 

[fixitflav]

I agree, but it still doesn't explain why there seems to be a difference in flow, or pressure, between the hot and cold.

If it's just a mixer, and another cold water outlet is opened the cold to the mixer falls. And if a hot tap is opened the shower would go colder. Might be worth the OP checking whether the effect is the same when any tap is opened.
Another question to the OP - does the shower stay too hot until the toilet refills, or does it recover? Because even a thermostatic shower is likely to get a blip in temperature.

 

[kofi2003uk]

shower stays hot until toilet fills up and then its back to normal. i suspect the shower is just a mixer but i will look into it. thank you all

 

[JohnD]

If only the pipes were accessible, you could fit a pressure-balancing valve in trice.

 

[kofi2003uk]

i have got my plumber coming in later this week so will see the options. the pressure balancing might work- will discuss with the plumber . thanks chaps