New thermostat, old problem (wiring issue?)

[Karolisko]

Hi

I wanted to ask your advise, in case I missed something obvious, before I call someone in.

We have moved in to a new place, which had a Honeywell t6360b (and combi-boiler Main 24 HE) installed. The problem from the get go was that t6360b was useless as a thermostat and functioning only as a switch to turn the boiler on (when set to 25 degrees) and on (when set to less than 25 degrees).
I assumed that the thermostat was faulty and as I also fancied something more modern (but didn't need a smart thermostat) I have bought Honeywell t4 to replace it.
I have installed the new thermostat but as it could not controll/connect to the boiler I quickly replaced it with the old unit.
Is the wiring (old one on the boiler side, or new one-on t4) incorrect?
My old thermostat's wiring and cover plate are shown in the photos.
I have connected 1 to A, 3 to B in the new unit and isolated earth.
I did not open the boiler as I didn't feel confident enough but I'm happy to open it if I know what I'm checking for.
Timer on the boiler is set to constant.

Thank you for any ideas.

 

[ian1182]

There are not many choices for the T4, it's A & B to be connected. The older T6360B in theory should be 3 wires including a neutral in 2 as well as 1 and 3 connected. Is your T4 the non-wireless model or the wireless T4R? Not sure what you meant by "I have installed the new thermostat but as it could not control/connect to the boiler I quickly replaced it with the old unit".

I wonder if you have a more fundamental problem. One way you can check if the thermostat wires actually control the boiler would be to place the blue & brown into a common terminal, i.e. effectively setting the thermostat as permanently on. Naturally turn off the central heating at the fused spur first. If the boiler fires up then the cable is ok, if it does not then you probably need someone to check further.

 

[Karolisko]

Thank you for your reply Ian.

It is a non-wireless model.

To simplify my confusing sentence :
1. I have replaced t6360b with t4
2.T4 could not start the boiler
3. I have replaced t4 back with t6360b as it's cold outside and I need the boiler running.

I will try your idea (probably only later in the week) and report back.

Thanks again.

 

[ian1182]

Thank you for your reply Ian.

It is a non-wireless model.

To simplify my confusing sentence :
1. I have replaced t6360b with t4
2.T4 could not start the boiler
3. I have replaced t4 back with t6360b as it's cold outside and I need the boiler running.

I will try your idea (probably only later in the week) and report back.

Thanks again.

If the T6360B is starting the boiler that implies the cable is OK, so probably no need for my original suggestion. Your T4 could be faulty. Do you have a multi meter? As the T4 is battery powered you can check for continuity between A & B when it's scheduled to be on (time & temp). That can be done stand alone without needing to connect to anything.

 

[Johntheo5]

The T4 is programmable? so maybe its being supplied by the (if installed) original programme. Check for 230V at L

 

[Mister Banks]

Thank you for your reply Ian.

It is a non-wireless model.

To simplify my confusing sentence :
1. I have replaced t6360b with t4
2.T4 could not start the boiler
3. I have replaced t4 back with t6360b as it's cold outside and I need the boiler running.

I will try your idea (probably only later in the week) and report back.

Thanks again.

The T4 is a programmable thermostat whereas the t6360 is a dumb thermostat. If you install the T4 you will need to set your existing programmer to permanently on and adjust the heating schedules on the T4

 

[Karolisko]

If the T6360B is starting the boiler that implies the cable is OK, so probably no need for my original suggestion. Your T4 could be faulty. Do you have a multi meter? As the T4 is battery powered you can check for continuity between A & B when it's scheduled to be on (time & temp). That can be done stand alone without needing to connect to anything.

Good observation. However, as T6360B only started the boiler (and didn't function as a thermostat) I thought cables (or the way they are connected are at fault.
How can I check for continuity? (sorry, I'm not that experienced with DIY)

Thank you.

 

[Karolisko]

The T4 is a programmable thermostat whereas the t6360 is a dumb thermostat. If you install the T4 you will need to set your existing programmer to permanently on and adjust the heating schedules on the T4

Hi,
As I mentioned I have the boiler's programmer set to constant. I have raised the temperature on the T4 thermostat to 35 degrees and it had a flame icon on (calling for heat) but nothing happened.
Thank you.

 

[Karolisko]

The T4 is programmable? so maybe its being supplied by the (if installed) original programme. Check for 230V at L

Hi,
Yes, T4 is programmable. How do you mean that it is supplied by the original programme? I will check for 230V at L later in the week and report back.
Thank you.

 

[Johntheo5]

I mean the boilers programmer like you mentioned above, which you set to constant to try out the T4.
"However, as T6360B only started the boiler (and didn't function as a thermostat)" it certainly looks like a thermostat with that temperature dial, if you turn it up and down do you hear a click and does it start/stop the boiler?, these type of stats would normally have a hysteresis of ~ 1 degC.

 

[ian1182]

Good observation. However, as T6360B only started the boiler (and didn't function as a thermostat) I thought cables (or the way they are connected are at fault.
How can I check for continuity? (sorry, I'm not that experienced with DIY)

Thank you.

if you think about it, the T6360B thermostat is simply a temperature controlled switch. You only have two active wires connected to the thermostat, they are either open (heating off) or closed (heating on) when the programmer permits. The order of A or B on the T4 does not matter as it's just joining them together. Hence I don't believe the wires from thermostat location to boiler are the problem.

I see in another post you are checking for 230V, is that not with a multi meter. If so there should also be resistance settings and that's how you test for continuity.

 

[Johntheo5]

Hi

I wanted to ask your advise, in case I missed something obvious, before I call someone in.

We have moved in to a new place, which had a Honeywell t6360b (and combi-boiler Main 24 HE) installed. The problem from the get go was that t6360b was useless as a thermostat and functioning only as a switch to turn the boiler on (when set to 25 degrees) and on (when set to less than 25 degrees).
I assumed that the thermostat was faulty and as I also fancied something more modern (but didn't need a smart thermostat) I have bought Honeywell t4 to replace it.
I have installed the new thermostat but as it could not controll/connect to the boiler I quickly replaced it with the old unit.
Is the wiring (old one on the boiler side, or new one-on t4) incorrect?
My old thermostat's wiring and cover plate are shown in the photos.
I have connected 1 to A, 3 to B in the new unit and isolated earth.
I did not open the boiler as I didn't feel confident enough but I'm happy to open it if I know what I'm checking for.
Timer on the boiler is set to constant.

Thank you for any ideas.

View attachment 292769

Why are you showing a T40 above if you have installed a T4?, wiring diagram, below, which you do seem to have wired correctly as B should be the switched live to the boiler when there is a call for heat from the stat and the switch closes.

 

[RandomGrinch]

Why are you showing a T40 above if you have installed a T4?,

We have moved in to a new place, which had a Honeywell t6360b (and combi-boiler Main 24 HE) installed.

 

[JohnD]

The problem from the get go was that t6360b was useless as a thermostat and functioning only as a switch to turn the boiler on (when set to 25 degrees) and on (when set to less than 25 degrees).

Some sort of mistake in your wording?

The stat is supposed to turn the heating on and off. Like a switch. Do you mean it didn't?

 

[Karolisko]

Some sort of mistake in your wording?

The stat is supposed to turn the heating on and off. Like a switch. Do you mean it didn't?

Hi John,
I meant that it doesn't do it based on the temperature of the environment but only when I manually set moved the dial to 25 degrees.
Hope that clarifies it.
Thank you