HVAC Questions? Ask an HVAC Expert for Answers ASAP
Pilot light won't stay on, Baxi WM 40/4 RS, we can't get it to fire up either. The theromocupple has been replaced recently and has been working fine up to wddnesday evening, we've not been able to fet it started since then.
The boiler will not work unless the the thermocouple can hold the pilot light on after you let go
Can you ensure the pilot light is big enough to envelope the thermocouple tip
You can test the output of the thermocouple with a multimeter - about 30mV
If this is all correct and the gas valve will still not hold the pilot on then it it will be the gas valve at fault
I'm not sure we have a multimetre, but the thermocouple is new, it was replaced about 6 weeks ago.
You need to ensure the pilot light is big enough and covers the end of the thermocouple - can you see it?
Yes, the pilot light looks normal, the is no problem getting it lit, but it doesn't stay lit.
Does the end of the thermocouple sit in the flame?
Yes, I can see the thermocouple and theres a white coloured pipe going in next to it too i can see.
Is the tip of the thermocouple glowing red?
Is the end of the thermocouple in the flame?
But no red hot?
Not red hot.
If it is sat in the flame then it should be producing a voltage.
Where it connects to the gas valve, does it screw in the front or back?
Both thermocouple screws are at the front.
Got to do the school back in 10 minutes.
If the thermocouple screws in the front of the gas valve then it may screw into a "shoe" that has a couple of wires from/to it?
There could be an overheat thermostat in the circuit that may be faulty
Did the engineer that replaced the thermocouple say anything?
just have a look at what I have put and see if it makes sense?
Can you attach a photo of where the thermocouple attaches to the gas valve?
It just connects with a bolt top and bottom, no wires.
I have the GC no. now, so I will just dig out a diagram
Ok. I thought you bad given up hope!
Where it connects to the gas valve are there any wires - it is hard to see from the picture and some of these early models have overheat thermostats
Are no wires.
If the therocouple is glowing, which it isn't currently, would that be in effect creating a circuit for the system to fire up? I'm teying to get a better jnderstanding of how the system works.
The thermocouple sits in the flame
This creates a small electrical voltage of about 30mV
There is an electromagnet in the back of the gas valve
This electromagnet is powered by the thermocouple
When you push in the button to let the gas through and light it, the electromagnet holds the inside of that button
so when you let go and the pilot is lit it is held internally and you are only releasing the button and not the inside of the gas valve also
Once the inside of the gas valve are held open and you let go, it lets you turn the gas knob from pilot to main flame
With it being held internally you cannot turn the button
*without it being held internally you cannot turn the button
I'm not sure what do now in prder to source thd fault.
You may need someone to look at it.
You need to prove the thermocouple is producing the right voltage
If it is and screws directly into the gas valve then it will be a problem with your gas valve.
Can you not get the original guy back and tell him there is something wrong with the thermocouple he has fitted?
He would then need to look at it and diagnose the fault correctly
He should have checked the voltage from the old one and not just assumed that was the problem
Ideally I need a multi metre 1st then take it from there?
One that measures mV if you are going to tackle this yourself
I can't get an engineer until next week, I need to tey and get hot water for my children to bath lol.
But if you spend £30 on a meter just to find out if it is the gas valve at fault then you are no better off?
Do you not have an immersion heater?
We have a tank that the boiler heats.
Is there an immersion heater in the top?
I don't think so.
A round cover about 3" across and stands up about 2"
With a wire coming out of it?
Do you want to try another photo?
On top of the water tank?
Yes on top of the cylinder to one side of the pipe cominbg out of the top
No, no wires, only pipes. I need to go out for a couple of hours, I will contact you when I get back.
No problem, just come back on when you are back
Hi, sorry it took so long, I'm home for the evening now.
so you have no immersion heater?
No, the water is heated off the boiler.
if you have seen the thermocouple in the flame and the thermocouple is connected to the gas valve then it must be a problem with the new thermocouple or the gas gas valve
We have replaced thw thermocouple with a new one, irs still not glowing red or anything else... I dont know where the gas valve is?
The gas valve is the part wit the button that you push to light the gas and the thermocouple screws into
I see, its a whole unit, looks like we're going to have to get an engineer asap.
I think you have tried hard, but you are at the end of what you can do by yourself
I think you're right, thanks for you're help.