Combi Boiler with Shower Going Cold Intermittently

[Brian Johnson]

My 14 year old Worcester Greenstar 30 HE combi feeds my bathroom shower and the last two days when showering the water from the shower has gone cold for about 4 seconds, then heated up. Soon afterwards it again goes cold at the shower end for a few seconds, then heats up again, and the cycle continues.

Is this likely to be a boiler problem, or perhaps just a fault with the bathroom shower mixer thermostat? Could something be causing the boiler to cut out intermittently?

 

[AMGasServices]

What’s the hot water like in the kitchen, basin and bath taps ?

If it’s ok in other locations then you have an issue with the shower. Usually on a mixed shower it has scale buildup on the mixer cartridge. Best option is to replace the mixer cartridge.

 

[Harvest Fields]

As above mate. You need to test all other hot water outlets first. As it maybe a shower issue

 

[KarlD]

Hi Brian, It's obviously difficult to diagnose without looking at it but it sounds to me like the check valves may have gone in your shower mixer body. If either the hot or cold are feeding into the shower valve at different pressures a broken check valve may allow water to pass through the shower valve the wrong way, hot through to cold and vice versa which throws off the thermostatic cartridge therefore creating a fluctuating temperature. I use this site if I am struggling to ID the shower or its parts. Identify my Shower

 

[Brian Johnson]

Had my CH boiler serviced yesterday and the gas man reckoned it probably is the mixer unit, despite the fact it's only three years old. Thanks to everyone for their helpful comments. Can anyone tell me how to access the cartridge in this unit (see photo)?

 

[shaky]

Hi Brian, It's obviously difficult to diagnose without looking at it but it sounds to me like the check valves may have gone in your shower mixer body. If either the hot or cold are feeding into the shower valve at different pressures a broken check valve may allow water to pass through the shower valve the wrong way, hot through to cold and vice versa which throws off the thermostatic cartridge therefore creating a fluctuating temperature. I use this site if I am struggling to ID the shower or its parts. Identify my Shower

Hi Brian, It's obviously difficult to diagnose without looking at it but it sounds to me like the check valves may have gone in your shower mixer body. If either the hot or cold are feeding into the shower valve at different pressures a broken check valve may allow water to pass through the shower valve the wrong way, hot through to cold and vice versa which throws off the thermostatic cartridge therefore creating a fluctuating temperature. I use this site if I am struggling to ID the shower or its parts. Identify my Shower

On a bar shower you might as well replace in my opinion

 

[KarlD]

I agree with shaky, it would be less hassle to replace it. But I f you did want to open it up there’s probably a cap in the centre of each end, pick that out and you can then unscrew the handle, then you should be able to turn out the cartridges with an adjustable. Just make sure the shower is isolated