weil mclain boiler gv-4 short cycling

Lavishjim

I have a 1992 or 1993 weil mclain boiler gv-4 I m having problems with it short cycling fires runs for 15-30 secs shuts off and keeps repeating. I have changed the ignitor, vacuum switch, twice cleaned and checked vaccum lines, took apart PVC fresh air cleaned, took apart the PVC flue and had lots off rust in the flue where it attaches to boiler I blow it out cleaned. The boiler will run and get to temp only if I jump the Vacuum switch. I checked vacuum with a dual-port manometer I'm at 1.5 that's good. I cant figure this out please help!

JUGHNE

Did you look inside the boiler where the exhaust is connected?
It could be partially plugged.

Docfletcher

Did you clean out the holes the vacuum lines attach to at the fan housing?

Lavishjim

I took a bottle brush and ran in the pvc elbow that connects to the boiler exhaust about 10'' and pulled out chunks of rust.

Docfletcher

I think your speaking of a CPVC black plastic boiler exhaust. If your finding chunks of rust in there you should remove the elbow that attaches directly to the boiler. It's only one screw/bolt. Then you can see how bad the exhaust outlet is plugged or eroded as Jughne suggested.

Lavishjim

Yes sorry it is CPVC black plastic I did only find one screw on the bottom glad there is only one I was thinking there was more. I have not took the elbow off yet I will and let you know what I find. What is the best way to clean it out? Thanks

JUGHNE

Sounds like you might have a condensation problem.
That early series had an internal pump and thermostatic mixing valve to avoid cold return water.
Many mixing valves failed with the result of rust/condensation in the exhaust port.

What type of exhaust pipe does this have?

Docfletcher

Post well lighted photos of the cast iron hub so we can see the damage. Be aware that the Black CPVC plastic pipe is recalled and dangerous do to cracks and joint failure,

Lavishjim

Lots of rust. I had to shut it down it was short cycling and the boom! A explosion in the combustion chamber blow the fresh air intake off.

Docfletcher

Sorry to hear this. How old is the boiler? Have you given any thought as to what you will replace it with? My GV4 is 26 years old. Most likely I will replace it with another Weil McLain to make for an easier install.

Lavishjim

I just finished cleaning it out with a shop vac got lots of rust out put it all back together and it seems to running great. Its runs for 3 to 5 mins shuts off and pump keeps running. Before it would only run 15 to 30 seconds over and over again. It's a 1993 I'm thinking it will need replacing soon. I installed a old 80% forced air furnace last summer for air conditioning only was using it for a blower. I'm going to install a 95% + furnace next week for backup incase the boiler quits.

Docfletcher

If it acts up again... Maybe drop the inducer fan assembly, remove the cone and examine the flame side of the heat exchanger. Just a thought, not sure if it be worth the time to do it.

Lavishjim

Thanks for all the help!

JUGHNE

Where are you located?
I have a 1996 GV-4 series 2 spare boiler sitting in my basement. Also have the SS venting available.
Up graded to mod con.

Lavishjim

Michigan

JUGHNE

I am in northern Nebraska, probably too far.