Help please, replacing old Honeywell Room stat.

[DavidUK]

Just moved in...

We have a room stat that isn't reliable. Seems to have a wide range of on/off variance...







Red wire is 240v; blue is Zerov; yellow (not connected) is 36v.

Inside cover...



Boiler...



Controller...



We're having a new combi boiler fitted in a few months, just want to replace this stat to make the temp more controllable meanwhile.

This little stat, and its wiring, have me confused as to what to replace it with (cheaply!) as a stop gap, and how the new stat should be wired?

Any help as to what to buy (Screwfix, Wickes, nearby) and how to wire the new one would be appreciated.

Many thanks.

 

[MJPD29]

I would say that the blue is a switch live and that the yellow should not have 36v on it and should be connected to earth. Any basic 230v stat will do it, if it requires a neutral yellow can be used but make sure you identify the cables with the correct colours. And also sort out the cut earth

 

[Midwest]

Normally, Live (programmed on, red wire) would go to terminal 1, switch live (heating call) to terminal 3 (yellow wire) & neutral to terminal 2 (blue wire). But you would need to verify those connections at your wiring centre etc. If your current stat has no neutral connection, that might explain the imperfect temperature control.

A Honeywell T6360B would be a similar replacment, but there dozens of other similar stats.

I would suggest the 36V is a bit of a rouse; how are you measuring these voltages.

Edit; we have to be careful what advice we give, as we do not know of your ability or experience to carry out this work safely & correctly.

 

[DavidUK]

I'm using a testing screwdriver with a voltage scale in a window on it. Not the most sophisticated of devices!

Previously I have installed a new oil boiler, controller, cylinder and room stat but that was 25 years ago.

The other day, whilst wiring in a new hob I noticed the hob cable was 6mm2 but the cable from it's junction box to the cooker box was 2.5mm. I called in our sparky at that point to replace the 2.5 with 6mm. I know when things aren't right, as with this stat. If I get clear logical advice I may proceed, but if in doubt sparky's called out.

 

[buzzlightyear]

I'm using a testing screwdriver with a voltage scale in a window on it. Not the most sophisticated of devices

if I tell you they will take my sheriffs badge off me. seek advise from a rep sparky .

 

[davesparks]

The problem isn't the thermostat, it's the lack of a neutral connected to the thermostat which will be causing the wide gap between switching on and off.

 

[DavidUK]

Where has neutral gone?

 

[Midwest]

The problem isn't the thermostat, it's the lack of a neutral connected to the thermostat which will be causing the wide gap between switching on and off.

Tish tish, I've already said that

 

[davesparks]

Tish tish, I've already said that

Sorry, I missed that completely

 

[davesparks]

Where has neutral gone?

It was probably never there to start with.

 

[w0z]

to the OP
The neutral is needed to provide power for the tiny heater (resistance) in the stat, which in turn reduces the on/off hysteresis. Those stats are one of the most reliable ever made, a genius simple reliable piece of design in my opinion.

 

[DefyG]

This little stat, and its wiring, have me confused as to what to replace it with (cheaply!) as a stop gap, and how the new stat should be wired?

A 'cheap' stat will not be anymore accurate than the one you have so you may as well stick with it until the combi is fitted!

 

[jackhammerJIM]

2 options .
Find the other end of the 3 core and connect a neutral ...
Buy a stat with battery mains

 

[Midwest]

Or get a digital one like a Honeywell DT90E1012. They don't need a neutral.

Mind, I think the OP has gone long time ago.

 

[Toneyz]

Or get a digital one like a Honeywell DT90E1012. They don't need a neutral.

Mind, I think the OP has gone long time ago.

Have you not got your heating sorted yet?