No hot water from shower

[jackthelad]

I have a shower that runs off a combi. The shower has just started running cold even when shower tap on full heat. Combi is not firing up. When I run bathroom sink tap or bath tap hot water comes on.

This has been happening for a couple of days but I have just sussed that if I put the central heatiing on then switch the shower on the shower runs hot. While the shower is running hot if I turn the thermostat down on the central heating so it turns off the hot water in the shower turns cold as the combi switches off as if there is no demand for hot water.

 

[Puddle]

well you do not say make of boiler however sounds like hot water side of boiler requires a service or shower cartridge not opening enough and being to restrictive on hot side but sounds like first chose

 

[furryneddy]

Have you checked the shower head - is it clean ie. no limescale blocking the flow?

 

[frundle]

Remove head and turn on, also maybe a fault in the mixer control.

 

[jackthelad]

Hi thanks for replies, The combi is an Alpha CB28.

I made sure the thermostat for the CH was right down so CH was off and took the shower head off the hose, the water evetually came through hot. If I turned the Temp control knob on the Grohe shower controls to 40 (mid way between hot and cold) the water turned cold even though it would have been warm previously. I then turned the temp control to hottest setting again the water still stayed cold. Only when I turned the Water control Grohe shower tap off and on again the hot water kicked in again.

Is the shower cartridge burried behind the tiles or part of the hot tap.?

 

[frundle]

For what it would cost I would change the hot Cartridge which is often part of, and easily removable, the hot assembly tap. If you are getting hot to the taps it is looks like the mixer. At worse replace complete unit.

 

[jackthelad]

For what it would cost I would change the hot Cartridge which is often part of, and easily removable, the hot assembly tap. If you are getting hot to the taps it is looks like the mixer. At worse replace complete unit.

I have a Grohe twin tap shower Mixer where on the outside all there is are the two taps and an oval plate. When you say change the hot cartridge would that meen knocking the tiles out and busting the platerboard etc to access it.?

 

[frundle]

Take the plate off and unscrew the hot housing from the front cartridge will come out also if it is the old type.

 

[mcmoby69]

sounds like you have a split in your diaphragm in the diverter valve head in your boiler. if the shower gets hot when you turn ch heating on then its not yer shower.

try your shower with the hot tap running at the same time and see what that does. it sounds like when the shower is running it isnt creating enough flow thru the diverter valve head to move the diverter valve over. just summat to check before you start knocking tiles off.

 

[frundle]

I did not read your first post correctly. I would agree with a boiler fault and a split diaphram in the diverter or the switch on the valve. Biasi were renown for this.