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Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 20305
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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Have a Lochnivar Mini Fin boiler that won't light the

Customer Question

Have a Lochnivar Mini Fin boiler that won't light the burners when heat is requested Pilot light is always on, but can't get it to light the burners so the water is not getting heated but the pump is running
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: thermostats seem fine,
JA: Do you plan on doing the work yourself?
Customer: probably paid a guy to come out and get it going a few weeks ago, he said everything looked fine but doesn't seem to be working now. the boiler is for a radiant floor heat system
JA: Anything else we should know to help you best?
Customer: Just that the thermostats are requesting heat, the pump is turning on and circulating water, the boiler pilot light is on, but there seems to be some problem with getting the boiler to actually light the burners to heat the water ok
Submitted: 4 months ago.
Category: HVAC
Expert:  Rick replied 4 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

I need the actual model number for your boiler. Also do you have a multi-meter?

Customer: replied 4 months ago.
RVL90 model number
We think we have a multi-meter...
Expert:  Rick replied 4 months ago.

Ok, if you're on site now can you check to see if you have 24 volts AC to the gas control valve. In the mean time I'll look up the specs for your boiler.

Customer: replied 4 months ago.
not entirely sure what that is?
Expert:  Rick replied 4 months ago.

The gas control valve?

Customer: replied 4 months ago.
Just a sec lookiing on the gas control valve
Customer: replied 4 months ago.
Customer: replied 4 months ago.
26 volts if that matters
Expert:  Rick replied 4 months ago.

Yes, you have 26 volts (26 is OK) at the 2 terminals on the gas valve? If so and the pilot is lit then the gas valve should open and the burners should fire up.

Expert:  Rick replied 4 months ago.

If that's the case then the gas valve is faulty and needs to be replaced

Customer: replied 4 months ago.
There is a micro thermal switch (reset button), that we bypassed and they fired up...could the switch be bad and not sensing the pilot light is on (no heat)?
Customer: replied 4 months ago.
The valve seems to be opening and closing ok
Expert:  Rick replied 4 months ago.

If the valve was opening the burners would fire. Where are these switch leads connected.

Customer: replied 4 months ago.
Looks like One is coming from thermostat, the other is from the power supply
Customer: replied 4 months ago.
Not sure if I'm using the right terms, but could the switch where the reset button is be bad? That is what we're thinking since it works well when we bypass that switch...
Customer: replied 4 months ago.
It looks like a red reset button with a heat sensor on the back of it
Expert:  Rick replied 4 months ago.

If the leads aren't connected to a terminal block in the thermocouple (flame sensor in the pilot flame) or directly to the gas valve then that's not the culprit and if it's jumped out it's been removed from the picture anyway. If it's wired into the control circuit (like you seem to be describing) and it isn't jumped out now AND you have 26 volts at the gas valve then it's not the culprit

Customer: replied 4 months ago.
When we bypassed in and then adjusted the thermostat to request heat it lit the burners. then when we shut the thermostat back off it turned off the burners (again, while bypassed). It wouldn't do that when going through the switch (not bypassed)
Expert:  Rick replied 4 months ago.

Read my last response. What matters is what's happening now.

Customer: replied 4 months ago.
Ok, I guess I thought I answered that...if I didn't I guess I'm not sure what you're asking
Expert:  Rick replied 4 months ago.

If you have 26 volts to the gas valve now and the burners aren't firing then the gas valve is malfunctioning unless the switch you mention is connected directly to the gas valve or a terminal block in the thermocouple. It sounds like it's wired into the control circuit (which I would expect). If so the switch is not the current problem.

Customer: replied 4 months ago.
The switch is connected to the gas valve
Expert:  Rick replied 4 months ago.

Connected directly or via the control circuit? Is the switch jumped out now?

Customer: replied 4 months ago.
The switch wired seems to run to both the control circuit and gas valve
Expert:  Rick replied 4 months ago.

It's one or the other can't be both. Can you give me a picture of the gas valve?

Customer: replied 4 months ago.
It's not jumped now, but we've been messing with it. The switch makes the gas valve work, so that's what I mean when I say it's directly connected. It's tied into the circuitry for the gas valve. So it seems like if the switch is not satisfied the valve won't work. But if we remove it from the loop (bypass) the valve works.
Expert:  Rick replied 4 months ago.

What you're telling me doesn't add up. If the switch is in the control circuit, which is typical, and the switch is open (not working) then you can't have 26 volts at the gas valve. If jumping the switch makes the burners fire up and pushing the reset button on the switch doesn't help then you need a new switch.

Customer: replied 4 months ago.
trying to upload files
Expert:  Rick replied 4 months ago.

Ok, from what I can see the switch is in the control circuit and what I said before applies.

Customer: replied 4 months ago.
I'm not seeing how it couldn't be the switch if it works fine when that part is removed from the equation? The valve seems to be working just fine when the switch is removed from the equation -- it lights when it needs to and shuts off when it's supposed to...?
Expert:  Rick replied 4 months ago.

Then there's no way you can have 26 volts at the gas valve if the switch isn't working. The switch is in the circuit that supplies voltage to the valve. If the switch is open you would have zero voltage at the gas valve.

Customer: replied 4 months ago.
We checked opposite sides of the leads (ground and supply), through the switch (bypassing it)
Customer: replied 4 months ago.
I think we have it figured out, we're going to try this and see if it works long term. Thanks for your time
Expert:  Rick replied 4 months ago.

You're welcome