Run away boiler, now cast iron exchanger drips ...

[Tim Fastle]

RE: 1979 Burnham P206W, DOE 135000BTU, Natural gas, baseboard water boiler, 4300 sf home, 7 zones services just the heater.

So, about 11 months ago I woke up to a knocking and banging sound. I hurried to the mechanical room (inside the house) and found my boiler running and yet the temperature was at 220 degrees. I turned off the power and while the circulation pump went off the heat continued. I quickly pulled the panel and shut off the gas valve and it shut down. It was 4am and I had just jumped out of bed and was quite confused. With the gas off I turned the system back on so the circulation pump would come back on and at least pump water through the boiler to gradually cool it down.

After it cooled I fired it back up and monitored it closely and it worked fine, cycling up to 180 and down to 140 when heat was called for. It's a long story but I had the HVAC guy come out the next day and it worked fine for him. He told me that I must have been confused, that it was impossible for the gas valve to stay on with the power off. The circulation pump worked fine and purged the system for air but there didn't seem to be much. He said it was possible that it was the aquastat (LB8148-J-1009 Honeywell) but, having not experienced the problem, couldn't say for sure and it could be throwing parts at it. Not wanting it to happen again and thinking it really was the only logical problem I said to replace it. It worked fine for a couple of days but then ran away again. This time I paid attention and took notes. First I shut the power off , and indeed with the power off, the burners kept running. I turned the gas to the system off and let it cool. Then I fired it up again and it cycled fine. Over the next day I monitored the system the whole time it was on and every once in a while it would not shut off, even after I had turned power off. Long story short, I came to the conclusion it was a bad gas valve, ran it by my HVAC guy along with the pages of a log of temperatures and times I had been keeping for the last day, and he agreed (He also said that in over 40 years he had never seen that, a gas valve sticking open). We replaced the gas valve on the boiler and it worked fine. I still monitored it closely for the next month but it seemed to work fine and I considered it fixed.

Then, last night, 11 months later I wake up to a banging boiler. Same basic issue but, being 3 am and me in a hurry, I just shut off the gas valve on the boiler before turning it off so I can't say for sure if it would have shut off the burners had I turned the power off. I decided to let it cool down and then fire it up again after it cooled and monitor it to see if indeed it was, or would, run away. When I got ready to light the pilot I took a quick look around and noticed water in the pan under the burners. Upon closer inspection I can see that there is a drip that appears to becoming out of one of the sections of the cast iron heat exchanger - about 1 drip every 7-8 seconds.

So, my understanding is that this is a good quality unit and, while 40 years old, probably no need to replace it (leak not with standing). I assume that the sections of the heat exchanger can be replaced so that is probably repairable but I am not sure I want to do that. The truth is, this unit is scaring me and I am inclined to just replace it. The mechanical room is near the center of our house and the thought of what could have happened if I hadn't heard it running away or hadn't been home really worries me.

I guess I am looking for thoughts on a few questions and some advice. Is this thing repairable? Is it worth repairing (cost of that vs replacing) and any thoughts from anyone on why this thing is randomly "running away"? Because if I do get it repaired I want to fix that problem too. Could it be partially a clogged heat exchanger? I was thinking not because if the temp gets to 180 the aquastat should shut it down even if it is partially clogged.

Lastly, I am leaning towards just having it replaced with a more modern and, hopefully, better unit. By better I guess I just mean because it has more modern technology and manufacturing processes. After reading quite a bit of info online and in this forum, it seems like sizing is a bit complicated but very important and with a new unit I could, hopefully, get something that is well sized for my home and our needs although that sounds a bit hit and miss as well.

Well, this is long and I am sorry about that but any input, thoughts and insights would be greatly appreciated.

Thanks!

 

[Fitter30]

40 year old boiler they probably don't make the sections looking at a parts list looks like they sell sections together as one part. Don't know if the sections are gasketed or with slip nipples. Gas valves failing wide open would have to be rare they made fail closed have seen some leak through a little. High limit and operating control should of turned boiler off.

 

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[Tim Fastle]

Thanks Fitter, my HVAC guy said basically the same thing at the time, somewhere between impossible and very very rare for that valve to stay open. That having been said, after seeing it with my own eyes half a dozen times - power turned off and burner continuing to run until I turned off the gas - it was clear that, in this case, fail close was not working.

My HVAC guy said via the phone that he's fairly certain it's slip nipple and actually repairing the unit was difficult and not likely to work. He has been designing and installing radiant floor and baseboard water systems for 40+ years and seems to know his stuff but is a bit old school. I like him because he tends to want to keep stuff going and isn't at all about upselling or over servicing.

I think I am likely going to replace the unit. Our home is 4300 square feet and, again via the phone today, he said he would probably recommend a Weil McClain CGa-7, 180000 BTU unit. He also said, unless I am concerned with gas prices or what I am paying to heat, he would stay away from the High Efficiency units as they tend to have a lot of bells and whistles that aren't needed and tend to have a lot more things go wrong that result in service calls.

I took a quick look online and it looks like the Weil McClain CGa-7 at 175000 BTU runs about $3500. And idea what installation might run?

Thanks!

 

[Fitter30]

You have a 135,000 btu boiler at best 75% efficient. Why would you want to go bigger? It doesn't keep up at the dead of winter? Need to check with your gas company for any rebates. Existing boiler have outdoor reset? Windows, doors or insulation need upgrading. Electric company do they offer a energy audit with a blower door test?