Central heating issue.

[Bp89]

For some weeks now my central heating has been switching off after about ten hours and not refiring. The next morning the heating switches back on a timer and the same issue occurs after a number of hours. Occasionally the blue power light has flashed but on resetting, the boiler fires up and the heating stays on. There is no problem with hot water which always fires up and stays on so I suspected, some time ago, the Myson CH valve which I purchased. This morning the heating did not come on so I decided to change the actuator. After switching the power back on the boiler fired up and I had CH for about 15 minutes before, much to my surprise, the boiler switched off again. I have a Bosch boiler and a Sadia water cylinder.

Help appreciated.

 

[ShaunCorbs]

What’s the display temperature saying ?

 

[Bp89]

Thanks. There is no display temperature but I understand it could be a blocked condensate pipe issue. The replacement of the valve actuator wasn't necessary. There is water coming out into the waste pipe under a sink. I undid the pipe underneath the condensate trap under the boiler expecting a lot of liquid and 'bits', but nothing came out of the trap. The boiler will stay on for most of the day then lockout with the blue light flashing and restart after a break.