Combi shower temperature variation

[cabinscooter]

This topic has been discussed previously but not, I don't think, on our particular problem. We have a fairly new Baxi Combi which is regularly serviced which feeds a new Triton Benito thermostatic mixer bar. Whilst showering, it will suddenly go cold and then return to normal within a couple of minutes. At first, I thought it was a tap being turned on elsewhere in the house or the washing machine taking in cold water but this isn't the case ( I assume that is what would happen). The shower is described as Thermostatic but I thought perhaps it only prevents sudden rises in temperature to prevent scalding, not drops in temperature. It is a fairly cheap model so maybe this is what to expect ? It's not a major problem as you can feel it coming on and move away from the spray.

 

[jj4091]

Do you notice any temp variation at wash basin hot tap. If not then possibly the thermostic cartridge is faulty. It should maintain the temp at what ever you set it to. How new is new

 

[cabinscooter]

Not noticed any variation at hot taps but don't normally run them very long. Shower was new Jan 2026.

 

[denso13]

Run the basin hot tap while using the shower and check if it still goes cold.

 

[cabinscooter]

I'll try that thanks.

 

[cabinscooter]

Tried opening a hot tap while showering and it made no discernable difference . Looks like it's the cartridge in the shower bar not working very well. As I said, the Triton shower is only a few months old.
Another clue is that the newly installed H2O Low shower fitted to the bathroom taps (that Denso13 put me on to) doesn't vary in temperature and works well.

 

[gas112]

what model baxi and what age is it ?

 

[CarloHeatingEng]

Worth one check before you blame the cartridge. Next time it goes cold, have someone look at the boiler and see whether the flame symbol has dropped out.


A combi feeding a mixer bar at a low hot flow can overheat, shut the burner off for a minute or two, then relight. That gives you exactly what you're describing, cold for a bit and then it comes back.


If the flame is still on while the shower runs cold, it's the bar valve and you can stop looking at the boiler.

 

[cabinscooter]

Thanks, makes sense, I check that.