Gas boiler power supply

Wig

Hi, Boiler central heating does not work, DHW does work,

Are domestic boilers always powered with very little voltage? i.e. 0.3V?

The thermostat loop coming out of the boiler is at 38V - 44V depending if the loop is open or closed.

EDIT: see replies below, the voltmeter does not work, so all this talk about voltages is not reliable. However, see second quote box below on this post.

Also thermostat loop is earth, blue, red yellow, (blue not used).
I would expect to see at the boiler end wall, when red and yellow are disconnected from the boiler... and measure resistance in red and yellow..... (i.e. measuring resistance to and from the themostat.) I would expect to see open circuit/closed circuit depending if the room thermostat is on high or low temperature setting. But all I get is "Open Circuit" all the time...

There is a resistor in the thermostat housing.....

To bypass the thermostat can I safely bridge the boiler end of the thermostat loop? i.e. I don't need to worry that there is a resisitor in the thermostat housing? The boiler manual seems to indicate that this would be OK if you want to run the boiler continuously. see below.

The Boiler Manual
https://www.glow-worm.co.uk/glow-worm/cxi-range-157150.pdf

13 Fault Finding:
Diagram 13.1
"REMOVE THE LINK IF FITTING
VOLTAGE FREE OR 230V
SYSTEM CONTROLS.
IF THE LINK IS NOT REMOVED
THE BOILER WILL RUN
CONTINUOUSLY."

The strange thing is, although thermostat loop is always showing open circuit, it does show a voltage at the stat depending if the boiler is on or off. I guess this just proves that it is the return wire from the stat that has the break in it. The live wire from the boiler to the stat must be OK.

Thanks

shaun_from_Africa

The only boilers I've ever seen have always been 230/240v.

My first instinct is that you either have a faulty meter that you are using to measure the voltage or that you have it switched to DC instead of AC.

Alex1983

It will be mains power, don't understand much of what you said but if dhw is working then you have mains at the boiler and your issue is probably the room stat, refit the link to bypass stat/timer and I'm sure it will work for heating.

Wig

I'll test the meter on something with known juice.

But the meter shows the thermostat loop as 38V quite happily.

Wig

Ok the meter is faulty....It might need a new battery. LOL

But the resistance test is reliable, the meter works good for resistance test. SO the open circuit thermostat is what it is.

Alex1983

Some glowworm stats work on low voltage, just by pass it to rule it out. Refit the link and if it works for heating then you've proved the stat is faulty.

Alex1983

If the stat is open circuit when calling and satisfied then it's faulty

Wig

Ok. update,

As the manual effectively (but not explicitly) told me that you can bypass the stat with a link. I did exactly that... and the heating is now working...

:T

Now I'm waiting to see how long it will take for OH upstairs to come running down to tell me the heating is on !