Heating Help

Weil McLain GV-3 boiler issues..

I've got a question on my Weil McLain GV-3 boiler; I have recently, within the last three months, replaced the control board, venting, pressure switch and now the blower assembly, but still cannot get the boiler to run entirely thru its sequence. The latest error that I am getting is when the blower comes on, it runs for about five minutes, then the switch light starts to blink and the boiler shuts down. This is telling me that the pressure switch is not getting the pressure needed to close the contacts. If I jump out the pressure switch, the boiler fires and runs properly thru the sequence, at least until it has to relight, then errors because of the jumper. I also took the pressurized tube from the blower and blew in it when the blower was running to fool the controls that there was sufficient pressure. This allowed the boiler to sequence but I ran out of breath so it shut down. I've checked every connection, hose, barb connections, orifice, flue, combustion air intake and all were clear of obstructions.
Anyone got any ideas on what I should try next? Am I losing pressure somewhere else in the boiler? This is really turning into a costly little repair. Thanks for the help!

GV

You might have water inside the combustion chamber blocking the draft switch hose connection. Check for blockage. Blow out the drain lines.

could also check...

the fan motor for any build up on it. If there is, it may not generate the cfm's the boiler is looking for to pull in the pressure switch.

Missed something

Sounds like you need a new service guy instead of a parts changer because you didn't mention the a basic service like checking the burner cone. Remove it and flush it out with water and blow it out with compressed air before reinstalling with a new burner flange gasket. Also check the air inlet fitting, there is a screen and I've seen them clogged with Miller moths before. 

Also check the exhaust

It's difficult, but you can pull the exhaust connector off the heat exchanger and check for rusty stuff partly blocking the bottom passageway. Dig around and vacuum it out. Once it gets badly clogged up inside there is nothing you can do.

What altitude...

If above 5,000 feet, it requires a "special" pressure switch for applications at higher altitudes.

ME

use a manometer

to check the pressures. Is the gasket around the inducer ok, or is the screws loose? Once had a weird one where the gasket was bad, which wasn't causing a good seal, keeping the pressure switch from staying closed