Slow Central Heating & Boiler not always firing

I have had an issue that I have noticed for a couple of weeks now. When the central heating is set to come on in the morning the heating pump on the boilermate 2000 kicks in as expected and the radiators get slightly warm. Most mornings either the boiler doesn't fire up at this point or it does and then goes out after a short time still leaving the radiators cold. Eventually it will get the boilermate up to 60c to allow the heating pump to run again but the time it takes the boiler to fire can vary. Sometimes the boiler is completely idle for 30 minutes or more whereas other times it will fire up intermittently rather than constantly firing

Things I have checked so far:

The LED'S,Display on the Boilermate all seem ok. The Boilermate seems to be doing exactly what it should be doing in terms of turning pumps on/off and sending a switched live to the boiler when required.

When the issue above is occurring I have checked :
- The boiler pump is getting 240v volts with a multimeter
- The central heating pump is getting 240v volts with a multimeter when the LED is lit and the store temperature is showing above 60c
- The switched live going to the boiler is showing 240v volts with a multimeter

The issue only seems to occur when the heating hasn't been on for a while i.e overnight. Today the heating was also idle for around 4-5 hours and the issue again started to occur again when i manually switched the heating on again on the timer although not as bad as early in the morning.

During the day the store does seem to reach 74c when the heating has got hot or the thermostat has turned the call for heating off although i'm sure it is slower heating up than it used to be.

One other thing I have noticed tonight is that some radiators are much hotter than they usually are and others are much colder.

My thoughts so far are that the issue is either with one of the pumps not working correctly or the temperature sensor on the ideal slimeline classic se 15ff boiler is misbehaving. I am currently swaying towards one of the pumps as one of the temperature sensors has previously been replaced on the boiler. (I think it was the overheat sensor)

The next step I am considering is removing the screw from the middle of the boiler and heating pumps to observe how fast they are spinning. Is it safe to do this whilst the boilermate is running? I assume not too much water will come out?

The system is covered by British Gas but unfortunately last time they come out the store had reached 74c and the central heating was working so they refused to replace any parts.

I either need to get them to come out very early in the morning or leave the heating switched off until they arrive and hope the issue occurs.

If anyone has experienced similar symptoms and resolved the issue I would be interested to hear.

Apart from checking the pumps are freely spinning I'm at a loss what else to check without a Gas Engineer or British Gas here when the issue is happening....

The only other thing mentioned on posts on here is to check the system has enough water in. I wouldn't know where to drain water out of the system to ensure it refills from the header tank.

Thanks

Mark

This issue has now been resolved. It was the circuit board on the ideal boiler.

Thanks

Mark