Old Honeywell to New Thermostat wiring...

[stem]

That would work. However ideally, the thermostat should be supplied from the same 3A fused connection unit as the boiler so that all of the heating system components are isolated by the same switch.

If the thermostat was powered from a separate source, it would still be live when the boiler's fused spur was turned off. Whilst you are aware of that, anyone else working on the heating system in the future might receive an unexpected shock.

Looking your existing thermostat again, because of its age (circa 1980) I would imagine that it was previously used with a traditional boiler and may have only been wired to control the central heating pump or a motorised valve. Then when the new combi was installed the cable would need to be extended out to it.

 

[da3533]

yep makes sense... so terminals 3 is live, and 5 is neutral which has 240 volts... so easy to power up the stat from here.

15743699100817916200797039582658

• da3533
• 30 Oct 2020

Boiler 3 (L) to New Stat 4
Boiler 5 (N) to New Stat 3
New Stat 4 (L) connect to New Stat 1
Boiler 4 (SL) to New Stat 2

This correct?

 

[da3533]

LIKE THIS?

 

[da3533]

Can someone confirm this, please? I want to take another go at this and rewire from scratch.

 

[CBW]

I’d piggyback the L and N at the boiler, then 3 to 1 and 4 to 2. Careful as you may need to carry out some safety checks after work on the boiler.

 

[da3533]

I was going to do that but I can’t feed a new wire as such, I have to use the same cable with brown, blue And earth.

would the above work?
Boiler 3 (L) to New Stat 4
Boiler 5 (N) to New Stat 3
New Stat 4 (L) connect to New Stat 1
Boiler 4 (SL) to New Stat 2

?

 

[CBW]

It should do, try it.

 

[Gasinayr]

Set your multimeter to ohms. disconnect the wires at boiler, connect between two in turn and switch the thermostat on and off to find the two that make contact, connect them to 3/4 and the remaining one to 5 ( neutral ) job done

 

[da3533]

I did the above and still nothing... so I went ahead and did a jumper between 3 and 4 ... turned on electric and heard a pop.... nothing turns on.
I have a vailliant Turbo max 282E.
I looked for a pcb images for this boiler and as standard, 3 and 4 are connected...

So why did it blow.

 

[CBW]

Stray strand of wire when connected?

 

[da3533]

Sorry, I don’t under stand .. just jumper from 3 and 4 ... I wanted to omit the thermostat, I just gave up and took it out.. so I connected 3 and 4...

The black cover over pcb shows a small diagram. See attached

 

[da3533]

I did not do anything apart from remove the 3 and 4... made a small jumper wire from 3 to 4... even a new pcb on ebay has the same... see attached.

 

[denso13]

So why did it blow.

It should have been ok but who knows why it blew, something must have been touching something it shouldn't have.

 

[CBW]

Don’t know why it blew then, could be a fault elsewhere.

 

[da3533]

I’m buying a new pcb, only 30£ ...
it’s my dads house,.. and I messed up his heating. I shouldn’t have touched it.. it was bad news from the start.

Pcb replacement seems straight forward?
Most are colour coded will take pics before too...