Worcester 24CDI Hot then cold flow

[GLP]

Hi, Recently my boiler stopped working and the gas would not ignite do to a faulty gas valve. This has now been replaced and since then the boiler appeared to be working correctly. However I have noticed that when I shower the flow will go from hot to cold then to hot and back to cold.

I have run the shower and watched the boiler to see that after a minute or so it will switch off, the flames go out and then the pump/fan with stop. It will then restart and carry on for a little while and then repeat the process.

Could someone explain what is going wrong? The temp of the water does not seem particularly hot before it cuts out and it did not do this before the gas valve went. I used to get a steady flow and temperature of water.

The radiators seem to be working with no issues.

Any advice would be greatly appreciated
Thanks

 

[electronicsuk]

Assuming it's not related to the gas valve swap, it could be a case of the boiler detecting an overheat condition. This may be due to a scaled up plate HEX, or possibly a faulty thermistor/TC. I'm sure the experts will be along to better advise soon...

 

[Homesafe]

Have someone look at your DHW heat exchanger it seems like it has scale/sludged up.

This symptom is typical of this problem.