Honeywell T40 wiring

[steviemo]

Hello,
I'm looking to replace my thermostat with a digital one that can be programmed. The current wires are-

Earth on the left
Blue on term 2
Yellow on term 3
4 not used
Red on term 5

My new thermostat has only 3 pins to connect - it has the number ME83H, I think it's a generic one as there are a few different manufacturers....thanks

NC, COM and NO and is also the battery type.

Can anyone please explain which wire would go where and what to do with the wires not used ?

 

[CountryFan]

Red from terminal 1 (not 5) would go to Com, yellow in terminal 3 would go to NO, NC not used. Using connector blocks or similar park the neutral in one block and CPC/earth in the other. Or if your new stat has an earth parking terminal use that.

 

[steviemo]

Hi. Thankyou so much for the quick reply, the search feature did bring up similar but I wanted to be sure. This is the new one - it dosent mention mains suitable so was a bit worried -Thermostat thanks Steve

 

[CountryFan]

Hi. Thankyou so much for the quick reply, the search feature did bring up similar but I wanted to be sure. This is the new one - it dosent mention mains suitable so was a bit worried -Thermostat thanks Steve

It may not be suitable for mains and doesn't say this in the description, a bit poor imo. States unsuitable for electric heating and valves/actuators - this could be their way of saying, again poorly worded/described. If you're in any doubt - plenty of battery operated thermostats available that support mains/dry contact/volt free

 

[steviemo]

Thanks again, I might need to return it then

Steve

 

[Taylortwocities]

It may not be suitable for mains and doesn't say this in the description, a bit poor imo. States unsuitable for electric heating and valves/actuators - this could be their way of saying, again poorly worded/described. If you're in any doubt - plenty of battery operated thermostats available that support mains/dry contact/volt free

Wrong, mate.
If you care to look at the information (click on the words "see more product details") you will find a cornucopia of information.
Let me help...

Ity'll be fine if the heating system fuse is 3amp.

 

[CountryFan]

Wrong, mate.
If you care to look at the information (click on the words "see more product details") you will find a cornucopia of information.
Let me help...
View attachment 408600

Ity'll be fine if the heating system fuse is 3amp.

Thanks mate. I did look at the more information, I just missed the bit about product specifications, as that was a few extra clicks, which is more key than some other stuff that precedes it.

 

[steviemo]

I will check that later. Thanks. Just out of interest, whats the worst that can happen if it's not suitable and I wire it as advised?

 

[Taylortwocities]

I will check that later. Thanks. Just out of interest, whats the worst that can happen if it's not suitable and I wire it as advised?

If its not suitable, You send it back to Mr Bezos as not meeting the specifications. It'll be fine.

 

[steviemo]

will do ! - I only meant will it melt and drip down the wall or blow my boiler up.

 

[Taylortwocities]

will do ! - I only meant will it melt and drip down the wall or blow my boiler up.

At its heart it is a simple switch. The electronics are powered by a battery, so no more likely to melt than a battery torch.
The only bit that has mains voltage are the switch contacts. Make sure the heating system has only a 3amp fuse in it (it should have that already) then the fuse should pop before the contacts die. But no resulting meltdown, fire, pestilence, frogs, earthquake, etc

 

[ericmark]

Ity'll be fine if the heating system fuse is 3amp.

I agree, it does seem odd to rate it 5 watts, that does seem rather low for the relay contacts, and high for power used. At least for digital (on/off) thermostats, would expect that for analogue (up/down) thermostats.

 

[Taylortwocities]

I agree, it does seem odd to rate it 5 watts, that does seem rather low for the relay contacts, and high for power used. At least for digital (on/off) thermostats, would expect that for analogue (up/down) thermostats.

Think they mean 5 amps....

 

[ericmark]

Think they mean 5 amps....

That would make more sense.

 

[steviemo]

Thanks for all the advice....I will be sure to post my results as soon as I've got around to fitting it