Help with Weil Mclain GV 4 series 1 nat gas boiler

Chevyjohn123

First off, I am no heating expert. I have worked on many heating systems, large and small, but I am not an expert. I got a call from a friend, no heat, no hot water (indirect water heater) and it’s Dec in NY. Not able to get service person out for at least a week. I took a ride out to see if I could at least see what was going on. He has an early 90’s Weil Mclain GV4 series 1 boiler. His version of what happened. First off, the system has had min problems and maintained when failures have occurred. He has boiler at one end of a long ranch home, opened a faucet at far end of home to get hot water to the shower. He forgot that he had opened the faucet and it ran for up to 2 hrs. When he heard some strange noises from the basement he realized what he had done, turned off the water and ran to the basement. The boiler was spewing steam from the vent on the side, water temp was at 220*, press was at least 30lbs, he turned the power off, which obviously shut the pump down and water was apparently flashing to steam in the unit, he ran to the other end of the basement fearing for the explosion that he thought was imminent. I looked things over, flipped the switch, boiler went through firing sequence and fired but circulator wouldn’t run. Let it run for a few min and shut it down. Boiler and pump area were at approx 100* and return piping started heating up but no flow to supply. I am not familiar with the mixing valve setup on this system. We changed the pump to see if that would make a difference to no avail, and after a couple firings, the unit wouldn’t fire at all. No trouble codes, power everywhere there should have been. After coming home and doing some reading, I am thinking the mixing valve had a melt down or some kind of internal damage. Any thoughts on how to proceed from here? The system has worked great for many years and the owner would prefer to repair it if possible or cost effective.

kcopp

Sounds pretty surreal.
Leaving a faucet on should have no effect on the boiler.
I would not try to restart this until someone who knows that boiler gets eyes on it.

EBEBRATT-Ed

Pictures may help us see what is happening

Jamie Hall

Well I would say the original primary cause was that the either the aquastat failed closed or, much less common, a final relay in the burner control failed closed or the gas valve failed open -- neither of the latter being unheard of, but not common, nor would I expect to see that as the initial failure since you were able to get the unit to fire later, even though the circulator wouldn't run.

You may, however, now have other failures to contend with, and you will need to go through the system, unit and control by unit and control, and determine if anything else has failed, and how.

I would note that anything electrical which got wet in the process will need to be replaced, as will the gas valve if it got wet.

Chevyjohn123

Final solution to the problem…..a service tech from a local hvac company did show up and went through the system. As near as I can tell, the pump relay in the ignition module failed causing the pump to quit working. Assume the boiler kept firing intermittently but no circulation causing issues with the tempering valve and a plugged up relief valve that failed to open made things very exciting! The tech went through the entire system, replaced the ignition module, pump, relief valve, air scoop vent and any other parts he deemed questionable. All working fine now. The cost was pretty high but the boiler is in great shape so replacement would have been much higher cost. Thanks for all the comments and suggestions….Happy New Year to all, hope 2022 is a better year.