Heatmiser UH8-RF surge fuse is keep blowing up

We have underfloor heating installed with heatmiser UH8-RF and Grundfos UPM3 Flex As pump and Honeywll 272848 motorized valve.

It was working fine for nearly year and now it has started blowing surge fuse 5am 250v,(Fuse-2) in UH8-RF. Enire system is new and not sure why it is keep blowing surge fuse.

The person who installed it not willing to come now as he has moved to 200 miles away and before I call someone just want to know what could be an issue.

Many thanks,

Does it not work at all and blow the fuse as soon as powered up, OR seem to work but blow the fuse later ?

If you have no test equipment, try disconnecting the pump and motorised valve IMORTANT take photographs and document where and how they are connected so you can put them back the same.

If the fuse stops blowing, replace them one at a time and try again.

There are plenty of other things that can blow the fuse like a faulty UFH actuator, so trial by substitution could take a long time.

Locked to prevent being resurrected (again)