Weil Mclane furnace not kicking on

Old 01-25-12, 09:38 AM
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Weil Mclane furnace not kicking on

OKay, i got a weil mclane furnace at home
Gas, used for force hot water heating

model - CG series, discontinued.

The gas valve has been replaced along with the thermal couple.
This is what happens.

The pilot is lit, so i know gas is coming through.
The boiler does not pass the signal to kick the flames on to heat the water up.

I connected a thermostat directly to the furnace in place of the original to confirm it was not a thermostat wire issue.

A few days ago my sister hears a few loud bangs coming from the furnace.

Not sure what caused it, but probably why the flames will not kick on and again, pilot is lit

Had the plumber come over.
He replaced the gas valve and thermocouple.
Checked the limit vents.
He mentioned it maybe something with the relay.

I had ran out and bought a whole new relay\transformer to replace the one it had.

So, this is what i hear when i power it on.
First i confirm pilot is still lit.
I turn the switch on, the relay makes a click sound and then i hear the circulator pump run as well, then i can hear the water through the pipes, i crank up the thermostat to 90, no way it was even 70 in that room, and still the tubes below never ignite to heat up the water.

So, what am i missing to check here?

Any suggestions would really be appreciated
Thank you
Old 01-25-12, 10:46 AM
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Is there an aquastat in the circuit that controls the burner? Most modern gas valves run on 24V, directly - no need for a relay. What voltage do you measure at the gas valve? If it isn't 24V, then you need to troubleshoot with a mulitmeter, and find out why. If it measures 120V, then I suspect you've burned up the gas valve coil.
Old 01-25-12, 05:32 PM
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Please tell us the full model number of the boiler... we need that to help any further.

There's also the 'rollout switch' and the 'spill switch' that could cause the problem.

The rollout in particular is most likely a 'thermal fuse', once it blows, it needs to be replaced. If it blows, it usually means there's a problem that needs correcting.

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