I need some advice on my Mira 415 shower

Does hot water temperature vary at the basin/bath tap?

A miracle :-) The cold water flow rate will drop to both the shower and the boiler so the temperature at the shower should remain fairly constant, but the flow rate could drop dramatically.

Charlie

Probably the thermostat module needs an overhaul. Even if the hot or cold stop the 415 valve will not change the temp by much. Unless its very old (20 years) the threads on the valve module are LH. You could undo it and descale it and see if that fixes it. Otherwise send it away to be fixed.

The Mira 415 is a pressure balancing shower mixer without thermostatic control. Therefore, the problem is likely to be either varying pressure on one of the supplies not compensated for by the pressure balancing valve. Or, more likely, there is an issue with the boiler not regulating temperature properly.

You are unlikely to improve the performance in this regard without extremely disruptive and expensive work. However, you can mitigate the effect by turning down isolator valves to the minimum acceptable flow for each outlet. There is no need for the toilet to fill in 20 seconds, or a basin to blast out the water. If you turn down these isolators, then the effect of using the tap/toilet will be reduced.

Christian.

The Mira 415 does not have a thermostat module.

Christian.

Have you read the manual for the shower?

david

Hmm.. My Mira 415 doesn't look like that. I wonder why they have reused the model number?

Sledgehammer the combi into tiny little bits and dispose of in an approved manner. Then fit a storage cylinder and a new (obviously non-combi) boiler. Problem solved .....zippo :)