For gawd's sakes... Thought I'd do a surf for 'pulsing' UPS2, and it seems it's (a) quite common and (b) a fault... Looks like these electronic jobbies are sensitive to electrical spikes and sh**. So it looks as tho' I'll have to replace the 3-porter, PCB AND the bludy pump! Jeepers. Something I don't understand about these pumps - you can set it to 3 fixed speeds like a normal pump, but you can also set them to 'proportional pressure' in each range. Ie, it'll spin as fast as needed, but will slow down when TRVs shut off and less flow is required. Cool. BUT, why would anyone set it at a fixed speed? Surely 'variable' is always the way to go? But there's no advice on this given in the instructions - it just tells you there's the option. AAAAARGH!