Replacing Drayton 3/4 wire thermostat. New BG one does not work in existing system.

[TMHM]

Hi Folks.
I am trying to replace a damaged 4 wire (L/N/E & Switched L) Drayton Invensys RTS1 Electronic Thermostat with a replacement BG WS4 Electronic version.
As can be seen from the attached pictures, both have identical wiring diagrams, however the WS4 will not work in situ. If I connect the WS4 to a separate mains circuit (3 pin plug) and use a light bulb as a load across N and CH On, it works fine, and the relay?? can be heard switching the bulb on and off, so I am happy that it works ok. Wire it up as replacement and nothing at all. no relay?? click, jilch. I cannot, for the life of me, figure out what can be the problem. The damaged thermostat, however is working but, as can be seen, has damage caused by the owner using a heat gun too close to it!

Can you help?

 

[ShaunCorbs]

Any chance of a pic of the new thermostat?

And did you change the existing backplate for the one that came with the bg one ?

Also a pic of the existing connection/ wires

 

[Gasmk1]

have you changed the base as well the original one looks like it has shorted at some point

 

[TMHM]

Yes, changing the complete unit. The base is burnt due to the close proximity of a heat gun, as stated.

Pics 8153 & 4 are of the old unit. 8155 is the rear of the new unit.

 

[ShaunCorbs]

Yes, changing the complete unit. The base is burnt due to the close proximity of a heat gun, as stated.

Have you got a volt/ multi meter ?

 

[TMHM]

Have you got a volt/ multi meter ?

Yes. That was my next step, but as both devices are mains powered and switched and the connection circuit appears to be identical, I havent checked voltages as yet.

 

[ShaunCorbs]

Yes. That was my next step, but as both devices are mains powered and switched and the connection circuit appears to be identical, I havent checked voltages as yet.

Check if you have voltage on 1 if you do

Join 1 and 3 / use a link wire should fire the boiler up if not fault else where

Prob tripped a fuse

 

[TMHM]

Check if you have voltage on 1 if you do

Join 1 and 3 / use a link wire should fire the boiler up if not fault else where

Prob tripped a fuse

I hear what you are saying, however why does the old one still work if put back ( I have had to refit it as the new one doesnt work). If there was no power on 1 then the old one wouldnt work. Same as if fuse blown.

All I am doing is isolating power, changing complete unit and reapplying power. Tiz baffling....

 

[ShaunCorbs]

I hear what you are saying, however why does the old one still work if put back ( I have had to refit it as the new one doesnt work. If there was no power on 1 then the old one wouldnt work. same as if fuse blown.

All I am doing is isolating power, changing complete unit and reapplying power. Tiz baffling..

If the old one still works there’s either a fault with the new one or a problem with the install

Pins making full contact with the backplate ?

 

[TMHM]

If the old one still works there’s either a fault with the new one or a problem with the install

Pins making full contact with the backplate ?

not sure how to check pins in situ.
To summarise:-
Old unit works when fitted on wall, but is damaged.
New unit works under test conditions. ie not mounted on wall.
New one doesnt work when fitted to wall.
Old one still works when refitted to wall.

That sounds like a problem with the install, however it should be identical mains power in both cases.

 

[Darren Jackson]

Is the new one a boiler plus control, therefore works slightly different than just on & off according to room temperature.

 

[TMHM]

Is the new one a boiler plus control, therefore works slightly different than just on & off according to room temperature.

It shouldn’t be. But I dont honestly know. It doesn’t say so online.

 

[Burger]

With the old one connected, are you able to turn it off? Only reading the Drayton one, it says the call will remain open I feel not 230vac, so as per @ShaunCorbs, you may need to test voltage?

 

[TMHM]

Problem hopefully resolved. Apparently the controller was faulty, so the thermostat should be able to be replaced now.