Weil McLain GV-6 Series 4 - Exhaust pressure issues

TwinLabs13

I have what I believe is a 13 year old Weil McClain (I'd have to double check the age). It's been recently serviced and everything checked out great. It's running a 5 zones of heating and they all work without any problems. Efficiency seems to still be running great too.

Here's the quirky issue we're having with it. On occasion, sometimes once a day, sometimes every few days (and for no apparent reason), the exhaust will, for a lack of better term, "backfire". It's sometimes just a small pop like you're popping a plastic bag, sometimes it's a little bigger (usually startles the dogs). It'll happen at the start of the cycle or at the end. There's nothing consistent about it. Right now it's more of an annoyance since everything seems to work fine otherwise.

Usually what happens is it pops the cap off on the outside vent. It was doing this about once a week when the weather was warm and we weren't using the baseboard heating, so we had it serviced. I checked to make sure there was no blockage in the exhaust. The old vent pipe gaskets were in bad shape, so those should be replaced, and I did re-tape the pipe since the old tape was crumbling. The only thing out of place is the hose trap return line, the connection was corroded and is not properly attached.

Any thoughts would be greatly appreciated!

JUGHNE

What type of vent pipe is this, PVC or stainless steel?
Is that drain right at the boiler exhaust port?
Has the burner cone been inspected and cleaned?

TwinLabs13

Here's an image of the tube I'm referring to and also an example of what sometimes happens. It was recently serviced so I believe that the burner cone was inspected and cleaned at that time. I also just noticed some black residue that had been dripping from what I believe is the expansion tank air vent/pressure release valve. Just a small amount looks like it's dripped down the side of the expansion tank, but that seems to be relatively new.

JUGHNE

Could you step back and show a picture of the entire boiler, floor to ceiling. Several angles/sides of the boiler.

TwinLabs13

Here's a few more angles for you:












You can see the black residue that has dripped down near the pump at the bottom of this image.

unclejohn

There should not be tape on your exhaust pipe. Did you tell the tech about the delayed ignition or just call for a service. You need to find the cause of the delay ASAP.

TwinLabs13

99% of the time it fires normal, no issues. Therm usage the last few months is consistent with year on year comparison. We mentioned that it was acting up, so it was a general service/cleaning call. He test fired it multiple times with no issues. That tape was on there since we bought the house 4 years ago (passed inspection and was also evaluated through MassSave for energy efficiency).

TwinLabs13

FWIW it was the igniter. Even though it would fire off and stay lit most of the time, it would intermittently cut out. The resulting gas build up, which wasn't much, was enough to cause the pipes to separate. Unfortunately for me, even after the second visit from the HVAC technician they didn't solve the primary issue. Between the cleaning service, the second visit (replaced the expansion tank as that was failing), replacing several of the exhaust pipe sections that needed it, plus the igniter, that was about a $900 investment. But.. it should last a long time now.

ScottSecor

Occasionally the ignitors fail due to the mini-explosions that were occuring. Hopefully the fuel to air mixture is proper and your problem is fully resolved. I agree with other, If you notice the delayed ignition again (fuel enters chamber then ignition occurs after a few seconds - should be instant) have it serviced immediately.

JUGHNE

I believe the igniter is also the flame sensor. It may always glow.....but it does not always know ( about flame sensing)

lchmb

one would think that some of these issue's would have been dealt with or scheduled at the time of service. I'm a big fan of replacing ignitor at every service. If they did the expansion tank did they also verify the P.R.V was working?

CarlWillms

I finally found information on my mystery vent pipe explosion in this thread. I also have a Weil McLain GV-6 Series 4. The vent pipe explosion happened only once about a year ago (that I know of); the vent gas explosion separated one pipe section and blew off the outside vent cap. I called a local boiler service company, and the boiler technician had no clue, and the condition could not be duplicated.

Recently, I have noticed an occasional strong natural gas smell outside in the discharge vent area. After the boiler automatically purges the gas, it refires correctly (no explosion). I have not been able to get to the boiler and check the control module LEDs, and since it only happens occasionally, the chance of the situation repeating during a service call is quite unlikely.

The ignitor replacement that appears to have solved the TwinLabs13 explosion issue may not be a cure for me, as I replaced the ignitor last December, a month or so after the service call. I plan to check the condensate drain and replace the ignitor again, but I wanted to check if anyone has any other ideas. Having a service tech charge me for not finding any problems and billing for a service call for no problem found is a waste of money.