Upgraded thermostat - now no heating/hw

[cb1980]

Hi,

Hopefully someone can help...

I just upgraded my old Rotary-style thermostat to a digital programmable one (Sunvic TLX6501 model from B&Q).

Since connecting it up I have no heating or hot water.

The pilot light is out, and I have already tried replacing the fuse in the switch above the boiler, but still nothing.

Is there anything I can do or do I need to call someone in?

Thanks!

 

[D_Hailsham]

Is there anything I can do or do I need to call someone in?

1. Check your wiring. Have you used the correct wiring diagram in the Sunvic Instructions?

The Sunvic is a combined thermostat/timeswitch so what have you done with the old timeswitch (assuming you had one)?

 

[cb1980]

Thanks for the reply!

There's a timeswitch on the boiler itself, which is set to non-timer mode. It's a Biasi (24S?) combi boiler by the way.

The wiring diagram on the Sunvic instructed me to connect "live" to the "COM" terminal, and to connect the "heater/cooler" in series with "NO" terminal and "neutral".

The Honeywell (T40?) rotary thermostat was connected in the following way (I took a photo before disconnecting anything, so I'm sure):
(L-R across the top of the unit, numbered as on diagram inside cover)
Earth: Yellow/Green
T2: Nothing
T3: Yellow
T4: Nothing
T1: Red

There was also an unconnected blue wire.

The diagram on the inside of the Honeywell 'stat cover shows Terminals 2 and 3 in parallel with 'N' (with a 3A fuse in series between N and terminal 3), and Terminal 1 connected to 'L'. I assumed 'N' and 'L' were Neutral and Live respectively and so connected the Yellow wire to 'NO' and red wire to 'COM'. Earth and Blue were left unconnected.

Any ideas?

 

[cb1980]

Anyone?

 

[D_Hailsham]

Your wiring certainly seems correct: The red wire should be in the Common (Terminal 1) and the Yellow in NO (terminal 2).

Do you have a meter (or borrow one!) if so, check that there is 240V at Common all the time and that there is 240V at NO when the CH is on and the thermostat turned up. Turning the thermostat up and down should, of course turn the 240v at NO on and off.

If this is OK, you need to find the other end of the Yellow wire and carry out the same check. After this you should trace the path from the yellow wire all the way to the boiler and check for 240V (on/off) at each junction.

 

[cb1980]

I don't have a meter.

The cable from the thermostat goes through the wall and up into the ceiling, then I assume it goes directly along and down to the boiler which is at the other end of the kitchen. It's below a tiled bathroom floor, so I can't get easy access to it.

What could I have done wrong that would cause (what looks like) complete loss of power to the boiler?

All the switches on my consumer unit are still in the "on" position, and there's no loss of power anywhere else in the house, including the kitchen.

Thanks again.

 

[D_Hailsham]

I don't have a meter.

That's unfortunate

The cable from the thermostat goes through the wall and up into the ceiling, then I assume it goes directly along and down to the boiler which is at the other end of the kitchen. It's below a tiled bathroom floor, so I can't get easy access to it.

Typical

What could I have done wrong that would cause (what looks like) complete loss of power to the boiler?

One possibility is that the time switch in the boiler is causing the problem. It should be in the Continuous (1) position

It could of course be a faulty Sunvic. The best way to check this is to temporarily connect the red and yellow wires together at the Sunvic end and see if the boiler then lights. ( Don't forget to turn the electricity off while you connect the wires together )

If the boiler lights, then replace the Sunvic - presumably under guarantee.

If the boiler does not light then the fault has probably occurred coincidentally and you need your tame boiler engineer.

 

[cb1980]

Thanks. I'll give that a try tonight.