Calling all boiler peeps!!!!! boiler problem or shower

[buddlet]

My shower keeps going cold and I want to know whether I need to buy a new thermostat cartridge or if its the boiler. I will tell you more.
Rose not scaled up and pressure good. Still cold though when I take the rose off
Hot water in all taps in bathroom. Shower gets warm if hot tap in sink left on a bit. When I turned on the cold tap in sink as well the water in shower was very hot for a bit then went cold again. Happy to buy a thermo if thats what it is but if its the heat exchanger or something else in boiler then........
All experts please help Thanks Buddlet

 

[clf-gas]

faulty NTC or perished diaphragm.

which boiler is it?

 

[buddlet]

Its a Vaillant Combi - very good and effecient and I have no other trouble with it. Whats an NTC?

 

[Andygasman2010]

What model Vaillant? An NTC is a temperature sensor (negative temperature coefficiant)

 

[buddlet]

a combi compact 242 GE?

 

[scatmanjohn]

If all the taps are hot but the shower is not then i would suggest its the shower.

 

[buddlet]

Well the hot taps are fine in the bath and the basin once they run hot, takes a minute or so. The pressure is OK not brilliant in the bath. Just odd that when I turned on the hot tap (to a trickle) and the cold tap ( te reliev the pressure) in the basin the shower went really hot and then cold. The boiler does not seem to fire up when the shower is turned on. Thanks for this

 

[dreadnoughtheating]

Non-modulating combi's and thermostatic shower valves are a match made in hell, they are fighting each other. Effectively the boiler overheats, shuts down to recover, colder water continues to flow, thermo valve opens up fully allowing enough flow to kick boiler into life again, cycle re-starts.

NO easy answer to this sorry to say.....

DH

 

[buddlet]

OK.... but its been fine for 8 years and over the last couple of months the shower has been erratic. The boiler is about 11 years old..... Can anyone give me any tests to do so that I can pinpoint whether it is the thermostatic cartridge that needs replacing. Its a Bristan shower. Thanks all

 

[Agile]

The 242 modulates.

All the signs point to a faulty shower unit.

The cartridge might just need taking out and cleaning with something to deal with lime scale build up.

Tony

 

[buddlet]

Tony - we have taken out the cartridge and it's fine - all filters ok and scale free.