Froststat is wired to permanent live, from the boiler switch, is this right?

[Ron S]

Hi, May I seek advice?

House/boiler is mid-90's. I am updating my froststat (it physically broke internally and has been firing up boiler inappropriately) and I have found that it is on a PERMANENT live feed (on voltage checking) despite the boiler switch overriding its effect, (ie fully turning off boiler), so I presume that the boiler is on the switchable live. (Boiler switch appears to feed both boiler and separate froststatwith white cables).

Is this set-up wired correctly? I see no obvious reason the froststat should be permanently live, as the boiler switch definitely deacticates it (I have clearly shown this). So why would it be on a permanent live?

Should I rewire froststat to be switchable live? ...Also should boiler be switchable (as it seems to be) - or permanently live? Thank you!

 

[RandomGrinch]

You may be overthinking things!

fully turning off boiler

Do you fully turn off your boiler?
I know I don't!

The frost stat and associated controls should be connected to the same supply, i.e. the same FCU.
This ensures a single point of isolation for the C/H system.
It also ensures that the frost stat can call for heat from the boiler, if the temperature is too low and there is the risk of damage to the boiler.

There's some good information here...

Frost Thermostat wiring for central heating installations

Wiring diagrams for installing a pair of thermostats to prevent frost in water based central heating systems

flameport.com

 

[Ron S]

Yes I have had to use the boiler switch to deactivate the faulty froststat. Boiler would not switch off!! Hopefully shortly this will not be necessary when new froststat is fitted. But still the question remains what is the point of a permanent live to the froststat when the boiler switch cancels it out anyway? Also leaving froststat live is potentially asking for electrocution if tampered with if one was to think it was off at the "switch"...which it isn't.

From my reading, it seems maybe this is how older systems were wired, (due to lack of terminals in the swtch??) but modern boilers are permanent live and the froststats switchable I think.

 

[RandomGrinch]

Also leaving froststat live is potentially asking for electrocution if tampered with if one was to think it was off at the "switch"...which it isn't.

As I said earlier, the boiler and associated controls should be fed from the same FCU, for a single point of isolation.
There should be little risk of tampering, or electrocution. Anyone with sense would also test circuits for dead, before working on them anyway.

If you are still concerned, you could post some pictures of your system and wiring - we could then give a more considered opinion.

 

[Ron S]

I have now fitted the replacement froststat which just has one permanent live and the neutral. Froststat is clicking at ambient temp but boiler not activating.

 

[Exedon]

Clear pics of what you have done would be useful
You should really have a pipe stat wired into circuit as well.