Honeywell wall stat to Salus

PeeDeeTee · 18 Sep 2019

I'm changing my Honeywell T6360B thermostat for a Salus RT310 but am struggling to understand how the Honeywell is currently wired. The Honeywell website states
1 = Live
2 = Neutral
3 = Switched Live
but if you take a look at the attached photo the wiring doesn't match this. There is a brown wire to 1, a brown sleeved black wire to 2, nothing to 3 and a grey wire just folded up at the top.

Would appreciate some advice!

Thanks.

JohnD · 18 Sep 2019

https://heatingcontrols.honeywellhome.com/Documents/Installation-Guide/pdf/1151.pdf

I don't know for sure which model you've got, but it looks like it is connected (1) and (2)

not (1) and (3)

However if the system is currently working and the thermostat turns the heating on and off (DOES IT?)

then the two wires that are actually connected to the terminals must be the live and switched live.

If it doesn't currently work then all bets are off until you work out what the wires do.

PeeDeeTee · 18 Sep 2019

Hi JohnD,

Thanks for the quick reply. It's the T6360B.

Yes, if the heating is on at the boiler the thermostat works as expected. I'd assumed that 1 was the live and 2 the switched live but can't understand how it's working as 2 is technically the neutral terminal?

JohnD · 18 Sep 2019

2 and 3 are connected together, through a small resistor which warms up as current passes through it.

The thermostat doesn't need a neutral.

The wire must be heating load, or the stat wouldn't turn it on. It's not really the neutral, it's "neutral after it has passed through the heating system controls" which in your case is near enough for it to work.

PeeDeeTee · 18 Sep 2019

Thanks, so safe to assume that the brown sleeved black in 2 is the switched live and the brown in 1 is the live?
The Salus has 1(COM), 2(NC) Switched Live OFF and 3(NO) Switched Live ON.
How do these translate between the two thermostats? I understand that COM is the permanent live but which switched should I use and do I only need the two wires going into the Salus?

JohnD · 18 Sep 2019

PeeDeeTee said:
so safe to assume

no, test them. also preferably look in the junction box or whatever where the wires are connected into the boiler

(some boilers are sealed to prevent amateurs doing that).

I don't know the Salus instructions (I am a householder not a boiler person).

PeeDeeTee · 18 Sep 2019

OK, so I've used my multimeter and the wire at 1 has a permanent 240v. The wire at 2 has 0v with the thermostat not calling but once heating is called the reading goes up to around 45v. Does that seem right, being an amateur I expected to see 240v at the switched terminal once heating had been called.
I can see where the wiring goes into the boiler but I'd really rather not start to open it all up!

If I'm understanding the Salus wiring I need to connect live to COM and switched live to NO?Also need to terminate the unused earth and neutral wires?

Thanks so much for your advice on this.

ericmark · 18 Sep 2019

It seems a thermostat that looks like the Honeywell T6360B can have different internal connections, it seems likely it is connected 1 and 2 on first diagram instead of 1 and 3 due to voltage measured, however to change without being sure why it was wired that way I would not personally do without checking the connections in the boiler.

EFLImpudence · 18 Sep 2019

Isn't there a diagram on the inside of the cover?

PeeDeeTee · 18 Sep 2019

Does this help?

ericmark · 18 Sep 2019

Some boilers have the thermostat connected to a lower voltage either 24 (off/on) or 48 (modulating) and my worry is some one may have connected to the extra low voltage bit of the boiler, it is unlikely, however possible, so I would want to check what it is connected to on the boiler before telling you to correct the wiring.

undertrained · 18 Sep 2019

I’m probably being thick, as I don’t understand much about wiring, but I was told by Honeywell that it does need a neutral for the heat anticipator to prevent large temperature swings.

EFLImpudence · 18 Sep 2019

Yes, but if you don't connect the neutral it will just be like a thermostat without the function.

The temperature swings won't be that large.

ericmark · 19 Sep 2019

undertrained said:
I’m probably being thick, as I don’t understand much about wiring, but I was told by Honeywell that it does need a neutral for the heat anticipator to prevent large temperature swings.

In some cases the large hysteresis is a plus, the wall thermostat is used to stop the boiler cycling in the warmer weather, so to click out at 21°C and then not re-energise boiler until 19°C would be good, where the TRV is controlling the room temperature to 20°C maximum.

However would a boiler work if the 230 volt input only has 48 volt? If not then is would seem not connected to the 230 volt input, this is the bit that worries me, if some one has for some odd reason not taken the 230 volt output expected from the thermostat to the 230 volt input on the boiler but one of the other inputs, then that needs correcting at the same time.

Although with open plan houses we may use a single wall thermostat to control the whole house, most houses have doors on the rooms without vents in the doors, so each room is controlled independently with the TRV, the wall thermostat is not to control temperature but to start and stop boiler when weather cools or warms up.

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Honeywell wall stat to Salus

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