Aquastat won't shut boiler

Peteys

I'm having a problem with my Aquastat, I believe, whereupon thermostat being satisfied, boiler will continue to run. Today temp rose to 80 degrees and would only shut down with me lowering and raising Aquastat. Had same problem with old Aquastat. This is a new Aquastat with a new well, with the special silver grease applied to Aquastat themocouple. Any ideas? It doesn't happen all the time. Maybe one a week. Maybe air bound? Water level is above Aquastat.

Much appreciated.

SWEI

Have you verified that the thermostat is actually opening the TT terminals on the boiler?

Jamie Hall

Keep in mind what your controls are supposed to do. The aquastat has nothing to do with the house temperature. That,s the thermostat's job, and it would appear that there's yoor problem, eh?

Peteys

Swei, not yet. But pretty sure it's the Aquastat. I will verify.

And Jamie, yes, I'm am aware of that but if the Aquastat isn't sensing water temperature it will run contually thereby raising the temperature in the house, no?

Jamie Hall

No -- the boiler might run continuously (until some other safety intervened) but the thermostat should control circulation to the house.

BobC

Verify the aquastat has failed by measurement before replacing it, otherwise you will end up with a spare on the shelf and a hole in your wallet.

I'm not saying it can't be bad but it would be uncommon.

Bob

Randy-LeeBraman

I would start at the thermostat,a easy test would be hook one side of it up with a jumper wire with alligator clips on each end.when you think its stuck just unhook the jumper ,this will let you know if its the thermostat or the aquastat,the norm is the aquastat just don't work,don't think i've ever had one that kept the boiler running,unless the contacts are fried closed.

Peteys

Yes, Bob, you're right. They hardly ever go bad. That's why I think it may be airbound or maybe the water from amtrol return is cooling it.

Think I already have a spare as there was probably nothing wrong with old aquastat. Gonna see if I can possibly move aquastat to another location as it may not be sensing water temp correctly where it is now, all the time.

Too much heat, better than no heat, I guess.

Peteys

Randy, I just got lucky today that I was around when this happened. Doesn't happen all the time.
If I was there when it happened again, I guess I could just remove a red or white from thermostat and if burner stopped, it's the thermo right? Not sure how to test the aquastat though, except for removing one wire.

Fred

You haven't done any work anywhere around the thermostat wiring, like nailing up some woodwork or other "nailing" related activities have you? I once had a similar problem, that was intermitent and after replacing the Thermostat and everything I could think of I decided to pull new wire from the Thermostat all the way through to the boiler. When I took the thermostat off the wall and a piece of door trim so I could drop the wire straight down, I found a trim nail right through the thermostat wire and when you stepped on a certian area of the floor, it put enough tension on the wire that the nail acted like a jumper. Just a thought.

Peteys

Fred, that's a good thought. Didn't replace low voltage wiring to aquastat. I'll do that next. Maybe a short there. Process of elimination at this point.

I'm using Bayweb and thought it might be the module, but the heat light goes off when thermostat is satisfied, but boiler continues to run. If it was my house, I wouldn't care and it would be easier to solve but it's a rental and there's a tenant there. Not so easy, especially when it doesn't happen all the time.

Peteys

I'm starting to think that it might be the module as the only time it ever continues to run boiler is after a call for heat. The boiler will run for hot water all day and never has it continued to run, as far I know, on a hot water call.

Peteys

May be b&g flow control valve not seated properly drawing cold water toward aquastat. Gonna replace on Monday. Thoughts?

Went there today and boiler was making steam, running continually. Lowered aquastat to 120 and boiler finally shut off.

Peteys

Just an update. Turned out the problem was the flow control valve. Replaced it and no problems since. Thank you for all the help. This is a great forum!