Boilermate and Potterton Suprima

The green light on my Potterton is flashing. It fires up for approx 5 mins and then shuts down for approx 15 mins and so repeats the cycle.
The water in the Boilermate is lukewarm (usually very hot). Radiators are lukewarm. Wall thermostat calling for heat. It has been like this since Friday night.
No noise coming from front panel of Boilermate. Have opened front panel and both circuit boards "look" ok (no scorch marks).
Both pumps on the Boilermate "feel" ok (both vibrating).
Have moved store temperature on Boilermate to Max.
Had the gas valve replaced on Potterton last month.
From the above (and thanks for reading), is there anything I can do before I call out an engineer tomorrow (I have a new delay timer, but the current one is not making any noise).
Also, do I call someone to look at the Potterton boiler or someone to look at the Boilermate (and my experience is that not everyone knows about both).
Thanks.

Could be the boiler
Or the unit.
Could be sludge in the pipe work
Could be Boiler pump in unit.
Check need to be made.
Mike
MGC/H2O
Norfolk