Noisy electrical underfloor heating

[Tonytonytony]

I have recently had electrical underfloor heating installed in a large room under porcelain tiling. Every five minutes there is a loud thumping sound from the CPN unit which is next to the off/on switch. Why does this happen & can it be stopped?

 

[stillp]

CPN unit

There's your problem!

 

[Echo the husky]

It's a contactor switching the elements on and off. It may be possible to change it to a solid state contactor which runs silently but you may need to incorporate additional overheat protection as they tend to fail permanently on which could create a hazard. what is the rating of the floor elements?