CH wiring query

[rich p]

I'm replacing an old central heating thermostat with a Horstman HRT2. I only have one wire going in and the wiring instructions are here
http://www.tlc-direct.co.uk/Technical/DataSheets/Horstmann/HRT2_I_U.PDF

Live to 1
Neutral to4
but what's going on with the 3 terminal?

Any ideas?

 

[slowmotion]

Terminal 3 is the switched live that turns the boiler on. If you have a motorised valve for the CH, the switched live from terminal 3 operates the valve. When the valve is fully open, a switch inside the valve sends a live to the boiler. It's a bit confusing. Do you have two motorised valves, one for CH and one for hot water?

 

[661-Pete]

You should have two wire pairs feeding into your hole in the wall, in both pairs one wire should be blue (black in older systems) = Neutral, and the other Brown (formerly red) = Live.

One pair is the supply from the mains - it should be switched on or off by the main CH isolator switch. Careful with this! Make sure everything is isolated before starting work, and make sure you have identified the pairs correctly.

The other pair is the switched output to your CH pump and boiler.
You should connect both Neutrals (blue) to terminal 4, and the supply Live to terminal 1, and the switched Live to terminal 3.

If you have only one wire pair coming into the hole in the wall, then this will be live only: the brown wire will be the supply Live and the blue wire (which should have a red or brown sleeve on it) will be the switched Live. In that case you have no Neutral and cannot use that thermostat - possibly the old thermostat was a passive one that didn't need its own power supply. In that case you'll need to seek advice from the supplier.

 

[rich p]

Thanks men.

Pete, that seems to be the case, only 1 wire, L&N.

Back to the drawing board.

 

[montage]

is your new hip conductive?

 

[Piemaster]

If you have only one wire pair coming into the hole in the wall, then this will be live only: the brown wire will be the supply Live and the blue wire (which should have a red or brown sleeve on it) will be the switched Live. In that case you have no Neutral and cannot use that thermostat - possibly the old thermostat was a passive one that didn't need its own power supply. In that case you'll need to seek advice from the supplier.

I've just fitted a DRT2 to a two wire system as above. The thing is basically just a thermostatically controlled progammable switch.

 

[slowmotion]

What model is the old thermostat, and how is it wired up? In the bad old days, it was quite common for electricians to use the earth conductor of a twin and earth cable to provide the third electrical conductor if the thermostat needed (1) a live, (2) a switched live and (3) a neutral. The proper way is to use a three core and earth cable under those circumstances.

 

[XmisterIS]

What you want to do it solder all the wires together in one big lump, then weld it to the radiator, plug it, and switch the bad-boy on!!!!!!

 

[661-Pete]

What you want to do it solder all the wires together in one big lump, then weld it to the radiator, plug it, and switch the bad-boy on!!!!!!

"Solder all the wires together" is good. 'cos then, as soon as you switch on, it'll trip out the circuit breaker (or fuse) in your consumer unit, and possibly the service fuse as well. Then you'll just have to call the electricity board people out, and pay, and hopefully they'll politely escort you off the premises in a straitjacket....

 

[XmisterIS]

"Solder all the wires together" is good. 'cos then, as soon as you switch on, it'll trip out the circuit breaker (or fuse) in your consumer unit, and possibly the service fuse as well. Then you'll just have to call the electricity board people out, and pay, and hopefully they'll politely escort you off the premises in a straitjacket....

I don't want no polite escort off the property! I'm goin' out kickin' and screamin' obscenities at people who aren't there!

 

[rich p]

I've just fitted a DRT2 to a two wire system as above. The thing is basically just a thermostatically controlled progammable switch.

Thanks, I'll let into that when someone will give me a lift to a supplier!

What model is the old thermostat, and how is it wired up? In the bad old days, it was quite common for electricians to use the earth conductor of a twin and earth cable to provide the third electrical conductor if the thermostat needed (1) a live, (2) a switched live and (3) a neutral. The proper way is to use a three core and earth cable under those circumstances.

I don't remeber and I threw the old one away some time ago! Silly me!

 

[ianrauk]

What you want to do it solder all the wires together in one big lump, then weld it to the radiator, plug it, and switch the bad-boy on!!!!!!

Now I would also suggest this, but also whilst standing in the bath with the taps running, with an electric heater balanced on the side to keep you warm. Don't forget to plug in the electric drill and leave it on the side of the bath also...you might need it to make robot movement noises like in those WKD adverts.

 

[threebikesmcginty]

Cut the blue wire rich.




No wait, the red one...

rich?

 

[ianrauk]

 

[rich p]

thanks you two! I expected nothing less