Thanks very much for that and yes, the link worked OK. I will order one.

However, my boiler has been running for nearly four hours now and not a trace of a spike/pulse on Routerstats and no re-syncs That is with the router plugged into the old house wiring and not the new to which the boiler is connected suggesting that the problem is transmitted through the wiring. Can't really understand why as all wiring ultimately goes back to the same incoming main but via a separate set of circuit breakers. The boiler circuit is new but the original wiring is 35 years old!

Could be something simple like a dodgy connection on the new wiring, might be worth reterminating and checking the connections.

True, but I think I will contact the gentleman that installed and certified the new wiring, first!!

In reply to a post by Andrew_W:

Thanks but I'd have to put a 13 amp plug on the boiler!!

Nothing technically wrong with this.
But always a danger of being switched off accidently !

In this weather you'd certainly know if it was switched off!!!

Use an unswitched socket!