Short circuited the room thermostat now radiators don't work

[nunesaf]

Hello
My first post here, thanks for your help in advance. I need help to understand which component of my heating system might have failed – everything seems to be working but the radiators don’t warm up after a small incident last night. I have a conventional boiler with an electric cylinder and a gas boiler that was working fine until last night I have accidentally short circuited the room thermostat: the Live and Neutral touched very briefly as I was plastering the wall where this was (long story).
Now as a result the programmer protecting 3A fuse blew and I have replaced this. Now the programmer comes on, I can turn it on, off, timer, once etc. The pump is working so is the electric cylinder, the gas boiler also kicks in but no heat at all in the radiators!
Do you think I’ve fried the programmer? Would you be able to advise me what/how to test ?
A rapid reply would be most appreciated as my baby daughter doesn’t need the cold

 

[muggles]

Sounds like you've either killed the programmer or the 2 / 3-port valve. To test you'll need to open up the wiring centre and get your multimeter out

 

[nunesaf]

Sounds like you've either killed the programmer or the 2 / 3-port valve. To test you'll need to open up the wiring centre and get your multimeter out

Thanks Andrew

I am probably more inclined now to the 3-way valve got cooked. I cannot find my multimetre (my house is a mess!) but I can borrow one tonight.

Thanks for the help and I'll keep you posted.

 

[stem]

It's possible that the hot water side of the system is starting the boiler and pump, but the live to the motorised valve controlling the central heating is not present. My guess is that for a reaction of a second, before the fuse blew, a large current was being drawn through the programmer and has destroyed part of it, leaving it open circuit.

If you are competent, it's easy to test with a multimeter, check for a live at the thermostat.

Depending upon where the short circuit occurred at the thermostat IE before or after the switching contact, it's possible that the thermostat is damaged. that can be checked in the same way.

 

[Madrab]

Yup, Sounds like the power isn't getting to the valve.
That would be by either it not being sent by the programmer or it is being sent and the actuator isn't running.

Either way a multimeter test at each end will identify which it is.

 

[nunesaf]

So finally managed to get the multimetre and these were the possible readings:
Orange with 230v
grey 84v
white 0v
all regardeless whichever i do with the programmer

I guess the programmer is at fault as the white would get up to 230v briefly.
would this be the right assessment you think?

Thanks

 

[ChrisR]

White needs to be 230 for heating.
Until you fix it you can latch the valve in the "mid" position, so as long as the boiler's on to heat hot water you can get some heat in the radiators.
If you turn the boiler stat down and the cylinder stat up, it'll sit forever trying to heat the HW and failing. The room stat will do nothing.

 

[Tipper]

I did the same years ago... ...the programmer circuit board was blown during the short as well as blowing the power fuse. New programmer fixed it.
(Actually I replaced the programmer then took the old one apart and bridged across the blown part of the circuit board with wire and a soldering iron. Kept it for a spare for the next time!)

 

[Madrab]

Good fault finding pic if it's a Y plan you have

View media item 88408

 

[nunesaf]

Thanks all for your replies I very much appreciate it.

Now then I have a new programmer and it still doesn't work.

I can get 25v ac on the white wire to the mid position valve! Should this be enough to excite the step motor? I don't understand what is going on here as the thermostat holds the remaining 200v... btw when I short circuited the thermostat this was fully disconnected
It's defying logic!!!

 

[twgas]

Maybe you've not connected the room 'stat correctly!

 

[stem]

Depending upon where the short circuit occurred at the thermostat IE before or after the switching contact, it's possible that the thermostat is damaged.

With the heating set to 'on' at the programmer and the thermostat not calling for heat (set low) what voltage comes in from the programmer to the live terminal at the thermostat?

Then, turn the thermostat up. What voltage is on he switched live terminal?

Or try this test. What happens if you join the 'live' and 'switched live' at the thermostat together. Does the heating come on then?

 

[nunesaf]

Now then, good news it is working and i have 239v on the white. How? I don't know. Some self healing took place during the night or it was the result of droping the room stat on the floor...
Anyhow I must something dodgy around the thermostat but it's clear the programmer and valve are ok. I now have a brand new programmer... that has no use!
THANK YOU ALL, quite an awesome bunch of people . Thanks guys as I couldn't afford to pay someone to come around. every job in this house has an (expensive) surprise