Gas boiler at 260deg after fill?!?

Jim R.

A few weeks ago I replaced a leaky air vent in my baseboard heat. All else was well at the time.

Initially I had really noisy pipes, presumably from air, but they quieted down overnight. Over the next few weeks the noise returned, now with a slight kettle sound from the boiler, and PRV bucket was very slightly wet.

I decided to completely empty and refill the system before replacing PRV. Got a little sediment out but not much. There are a few runs if black pipe to the copper baseboards. So far do good.

Fill the system, turn on the boiler, DHW zone kicks in and heats up. Little noisy with a small squirt from the air eliminator, so far so good.

Next the main floor (1 story ranch) kicks on but I can't feel the pipes getting hot. I go upstairs to check for noise, nothing, come back to see the boiler temp at 260 degrees!!!! It was not running at the time but still. Pressure was still around 18-20psi.

So I turned it off at the switch and opened the PRV to let some water out, which cooled it down.

It seems like the circulator isn't working. It is on the supply side. Pipes out of it are cool, but I hear it spinning.

Could the system be completely air bound?

Now the boiler won't come on at all, even with a call for DHW. Possibly it tripped some kind of limit internally.

Boiler is Buderus g124x , 74Mbtu.

Going to call repairman tomorrow and keep it off overnight. Just wondering if you guys have any thoughts on what I did wrong?? Thanks.

Jim R.

An update to this... It occurred to me that I did not fill the system correctly. I filled it as a whole and then drained out the air until I got water. I redid it this morning zone-by-zone and it seems to be fine. It went through a few cycles as normal, both heat and DHW. Water noise is at minimum now and getting quieter each cycle.

Still going to keep an eye on the pressure relief valve as it dripped a bit around 200deg. That was with some air still in the system so we'll see.

Last night when the system went to 260 deg it was in the matter of seconds. First it was as 140ish and less than a minute it was at 260 and the boiler was shutdown. I assume it's the aquastat that does that shutoff? I must have had a boiler chamber full of steam.

unclejohn

You don't need water temps over 180*. What type of aqua stat is on it.

Zman

This post is a bit scary.
You need to get the majority of the air out prior to firing the boiler. Adding water to a boiler making the sound you describe with a gauge measuring 260 is a very bad idea. Being in the same room is not such a good plan either.
There is just no way to know if the boiler is dry with red hot surfaces or air locked with a small steam pocket. With red hot surfaces, you could blow it up.
Normally you can let the air out of a cold boiler by opening the PRV while filling.
What kind of air eliminator does the system have?
Where is it located?
Pictures would help.

Bob Bona_4

I'm nervous too, if that's an accurate temp. Assuming Honeywell aquastat? No logomatic mentioned. I'd get professional eyes on it asap, could be a gauge inaccuracy, control failure/bulb not fully in well, control setting...not something to take lightly

Jim R.

I was freaked out when I came downstairs to see 260 degrees! I knew it was totally wrong and overlimit. It went very quickly (like a speedometer accelerating) from about 140 to 260 and then the boiler shut down.

I definietly did not add any water under these circumstances! FIrst thing I did was pull the relief valve (slowly) to let out steam and water which brought the temp down pretty quickly. The supervent was spitting a bit and blowing some steam too.

Looking back on my filling mistake.. I got hardly any air out of the upstairs zone but the DHW zone (at the same level as the boiler) was pretty good. That heated without issues at first, then the main floor call for heat came. I suspect there was so much air above the the system that the circulator couldn't start the flow. So whatever the boiler had it turned to steam and then it was dry and heating air.

I'm surprised the PRV didn't trip by itself in this circumstance. Pressure was low but shouldn't it trip on both pressure AND temperature?

Pictures below.

For a while the supervent cap was loose and it would drip. That's where the stains came from. System is about 10 years old and seems to work well. Probably next year we're going to upgrade our baseboard heat to panel rads as part of a remodel, so I suspect a lot of this will be ripped out. Hoping to keep the boiler and DHW tank though (buderus G124x and ST200 tank).

Jim R.

Aquastat is Honeywell 8141E set at 180. Water temp definitely goes to about 200 before it shuts down, which has always been normal operation.

Next steps... I'm sure I did the fill wrong and when the boiler was cold tons of air came out of the upstairs zone. It seems back to normal now. So I'm chalking it up to operator error and just going to watch the PRV valve to make sure its not spitting. So far so good, all dry in the bucket.

I suppose it wouldn't hurt to get an inspection and a new PRV at the same time. Was hoping to wait a few more months until the remodel...

unclejohn

You have a taco controller. is it pumps or zone valves. If zone valves you need to manually open them to bleed.

Jim R.

Pumps. One priority for DHW and one for 1st floor baseboard.

I closed one zone, closed the boiler return, flushed water all the way through the open zone from the fill valve till the air was out. Then did the other zone.

A little bit of air and some drops came out the super vent for the next day or so but it settled down and I tightened the cap.