Mains Relay

Given very very few things draw constant current, I'd expect a relay rated at 13 amps to cope with a higher switch on load? Although I've never actually seen a relay rated at 13 amps. 15 would be more common.

Indeed so. 13A is a very British thing. Most other countries in Europe think about 15A - or even 16A.

Nonsense! Calculating the repetitive peak current is irrelevant. Relay current ratings are RMS values. An immersion heater is a very benign load - it's AC-21 service [1] with no significant inrush current. A 16 A relay of reputable manufacture should be fine, assuming any sensible number of switching events per day/hour.

In message , newshound writes

OK, OP here. I'm going to suggest rubber mounting of the existing relay inside a box and see what happens. I think his relay is from China via ebay, so a better quality one might buzz less.

Searching for mains to mains SSR found this

but I haven't found a UK supplier.

Most of these SSR's seem to be lowish voltage DC input and I don't think I want to have him doing calculations and assembling rectifiers and voltage dividers.

And?

It's called Great Britain for a reason.

There is no such place as Great France or Great Germany.

EICR on a rented property

Got a few odd readings.

I then asked "Do you want me to test the cannabis factory in in loft?

I gave a link to one from RS earlier. I'd guess CPC and others will have similar.

I'd personally not use an SSR for this. They are more expensive and very much more likely to fail in practice.

Virtually all AC coil relays are noisy to some extent, but some are worse than others. For your son's situation I would recommend using a modular relay. These clip directly onto DIN rail and can be fitted into a consumer unit or anything similar. They are virtually silent.

Something like this: