Tristan mixer shower runs cold for a few seconds every two minutes

[poolballboy]

We have a Tristan mixer shower fitted in the bathroom, over the last few months the shower will run cold for a few seconds after a couple of minutes and then gain heat again. This will happen every 2 minutes until you finish your shower.

We had the combi boiler serviced, thinking this was the problem, the service engineer said it was more than likely the thermostat inside the shower as the boiler was working fine. So we had the thermostat cartridge taken out and cleaned of any possible limescale to see if that would help, unfortunately it didn't. So we bit the bullet and bought a new mixer shower from Tristan as the old one was getting on in age anyway. We had the new shower fitted last week, but the running hot and then cold problem still persists.

To confirm, the original mixer shower and combi boiler had been working fine for around 6 years, the problem only started out of the blue a few months ago.

The only two conclusions I can come to at present is that:-

a - the new shower is also faulty (highly unlikely)
b - the combi boiler is losing heat after a few minutes and then kicking back in again for a few minutes.

Is there any possible guidance people may be able to provide me on what to look for and check next?

 

[Whitespirit66]

Is there a light on the front to denote that the burner is lit? Does it go out when the shower runs cold? Also hold the hot water pipe under boiler whilst shower running. Can you feel the pipe cool then get hotter again?

 

[poolballboy]

Whitespirit thanks for your reply.

I stood in front of the combi boiler tonight whilst the wife ran the shower. Indeed the boiler does shut down at around 56 degrees. The cold water then reduces the temperature quickly to 42 degrees when the boiler fires up again. This happens every time the boiler reaches 56 degrees with the shower running. Any thoughts on what would cause this?

 

[Cgas]

What boiler? Make\model.

 

[Agile]

For the moment if you run the hot tap on a basin at half flow then the boiler may stay on and your wife can have a continuous shower!

Tony

 

[poolballboy]

Hi thanks for the feedback, it's a combi boiler vokera / linea 24.

 

[Agile]

For the moment if you run the hot tap on a basin at half flow then the boiler may stay on and your wife can have a continuous shower!

Tony

 

[poolballboy]

Thanks Agile, that's a nice little trick that works perfectly lol