low pressure glow worm compact 80e?

I was losing pressure so checked radiators and found a leak. Sorted that but each time I top up the tank the low pressure light continues to flash and it is losing half to one bar every 12 hours. Could it be to do with the anti frost thing which ignites during the night in -zero temps? Have spent a fortune in the past on new circuit board etc and it's only 5yrs old.