UK Frost Thermostat wiring

[Raptor0014]

Evening all,

Have been asked to wire one of these into a heating system that has no separate control (or valves) for HW & CH. Customer is going to be away and wants it wiring in to allow the heating to only come on when the temp drops to keep pipes etc from freezing.

https://www.draytoncontrols.co.uk/products/thermostats/rts/rts3

However I just want to make sure I have this right as not wired one in before.

I am assuming I just connect this to the perm L & N and call for heat in the control centre? If he switches the heating off at the usual timer control panel, will this still kick in and turn the heating on once the temp drops below the set value? The instructions just say L, N and terminal 3 call for heat.

Thanks

Carl

 

[James]

I would take the live feed from the input of the timer relay, (assuming it is 230v) then the output of the frost stat back to the call for heat input that the room stat feeds into.
basically you are creating a circuit that bypasses all timers and thermostats .

 

[timhoward]

I am assuming I just connect this to the perm L & N and call for heat in the control centre? If he switches the heating off at the usual timer control panel, will this still kick in and turn the heating on once the temp drops below the set value? The instructions just say L, N and terminal 3 call for heat.

Yep. Exactly as you describe. (Get some 4 core flex from Screwfix)

Funnily enough I did a frost stat today, I hope your one goes better!

In my case it was a freestanding oil fired Bosch Worcester and there were frost stat connections on the main PCB. The old frost stat had become damaged and had been removed by someone else, who put all the connections in wagos and then put them in a wago box. So I assumed that joining the brown and the black sleeved brown would fire the boiler. The problem was that it didn't!

I'd been hoping to avoid opening up a DIN rail box on the wall containing a contactor and working out what was going on, but I had to dive in. In this case there was also a pipe stat in series, so the combination of very cold room and cold pipes would fire the boiler until either pipes reached 30 or the frost stat reached 3.
Eventually I worked out that the N to the coil was connected to nothing, and then in turn worked out that whoever fitted the nest had thought it was surplus to requirements.
Then to cap it all, when I powered up again the flipping nest wouldn't reconnect, long story short was that it hadn't been charging and was virtually flat, but I messed around for 40 minutes before realising this was the problem.
I thought this was a 30 minute job - I was there 2.5 hours!

 

[oscar21]

You normally wire these in series with a pipe stat, so the frost stat turns the boiler on and as soon as the pipework gets hot then it switches it back off again, its only to stop the pipework freezing, not heat the rooms.

 

[James]

I prefer to have them as a 5 degree room stat. then it puts enough heat into the building to prevent other pipes like hot and cold domestic water from freezing.

 

[timhoward]

I prefer to have them as a 5 degree room stat. then it puts enough heat into the building to prevent other pipes like hot and cold domestic water from freezing.

If the boiler is inside this is what I do too.

The recent one I did had the boiler in an outbuilding so the room stat / pipe stat combo made sense.

Incidentally is there a good reason that I'm missing why a relay was required to close the frost stat terminals on the boiler, coil fed by the frost stat and pipe stat in series? I've never seen that before. At first I wondered if it was a clever time delay relay but it wasn't.