Heating on all the time

I've had a few problems lately (replaced PCB in Potterton Suprima 30 - lockout problem; replaced the Pump Delay Timer Pcb XB041 - buzzing & pump not working, replaced the BRAWA Mixer Valve - no hot water) and everything has worked lovely for the past 2 weeks. But now, the radiators are on full blast, even though they are not set to come on. The room thermostat shows the heating is off as expected. The boiler is set to max, and the boilermate thermostat has got the temp set about half way on winter adjusted to make the green light go out when it should. The boiler is firing up frequently and the boilermate is whirring busily (is that boiling water I can hear??). It only goes off for a few minutes, then comes back on again. What is making it come on and how do I stop it? It seems to run all night!!
Thanks for any ideas.

My sympathies with your Suprima Boiler and BM2 Sue.
You say that you have replaced the Pump Delay Timer PCB, but have you also checked the Pump Drive PCB (XB104)? Instructions for checking both PCBs are given in the BM2 Installation and Servicing booklet. This booklet can be downloaded from the Gledhill website.
Also, do you have a gravity check valve on your system and if so, is it working correctly?
Robin

Thanks Robin,
There isn't a gravity valve (the boilermate 2 is in the airing cupbaord in the main bedroom). I found the manual and will give it a read to test the other PCB - thanks for the tip. In the meantime, I've read and read and read about radiators coming on without being scheduled to. It's been suggested to me that it will happen if the water/system is overheating. I spent some time checking the green light again and turned the thermostat down on the boilermate 2 again (so we are now about half way down the red/winter gauge). The water is a bit less hot out of the taps, but still alright. The boiler finally turned off after 5 hours of running and now it seems to be back to normal. Most odd. I watch and wonder.....