Oil Boiler Over Temp

Dave_from_NH

I have a Burnham V-14A-T boiler for hot water & baseboard heating. It has what looks like a Honeywell R8182H AquaStat controlling it. There is a temp sensor for the AquaStat in the hot water side, a temp/pressure gauge on the heating side, and the thermostat ties directly into the R8182 (single zone heating).



All winter I've been having problems with the overpressure valve popping and spilling water everywhere. I thought it was a bad expansion tank (Extrol 30). Now that the heating season is over, I replaced that along with the boiler over pressure valve and the temp/pressure gauge (the pressure gauge wasn't working).



I'm still getting over pressure conditions but I believe I have this narrowed down to a bad water feed valve. I think it's stuck open and allowing direct town water pressure into the system. Going to change it today. I have the shutoff valve closed to keep the pressure in the 12-18 range (used the overpressure valve to bring the pressure down).



The problem is that the boiler now goes into over temp (it never did this before). The AquaStat is set for a low limit of 160 and a high limit of 180. The thermostat is off so if I understand it correctly, the low limit is what should be active now. The boiler will happily climb up to 210 before I panic and turn it off.



I thought it might be an air pocket around the temp gauge so I tried opening the air bleeder on the boiler but I didn't get anything out of it. If it is is an air pocket, do I need to replace the feed valve before I can purge it? Do I need to turn the heat on to run the circulating pump?



The only other things I can think of that it might be is a bad AquaStat or temp sensor but they'd been running fine all winter.



Help! What am I missing?

Steamhead

Does the boiler have a tankless coil?

if so, it could be leaking and cooling the sensor so it wouldn't read the actual boiler temp. Time to call a pro- check the Find a Contractor page of this site. 

Dave_from_NH

Tankless Heater

Yeah, it does have the tankless heater installed. Is this a common failure on these boilers? Do you have any idea what a ballpark figure for replacing it would be?

Steamhead

We don't discuss pricing here

and it would be pointless to anyway, since we haven't verified the coil as the problem.



If the coil is bad, consider upgrading to an indirect tank which will give you more hot water at less cost, since there is more heat-transfer surface and you won't have to keep the boiler hot all the time. Indirects cost more, but perform much better so it's worth it. And, when the time comes to replace the boiler you can still use the same indirect.

Dave_from_NH

Tests

Oh, sorry about the pricing question. I didn't realize.



Well, I did a couple of tests. I hadn't changed the feed valve yet but I opened the shutoff for it. The pressure rose to about 15 and stayed there.



I also lowered the low limit to 140 on the AquaStat so I could test it faster. Once the gauge read 140 I shut off the valves for the tankless heater. My thinking was that if there's no incoming cold water the water in the heat exchanger would stabilize at boiler temp. But the furnace kept on running, I turned it off at 190. So I think this says the tankless isn't leaking, correct? The pressure also stayed around 18 when the system came up to temperature.



So I think I'm back to an air pocket around the temp gauge (which doesn't make sense because the pressure gauge seems to work correctly), a bad temp sensor, or a bad AquaStat.



I assume the temp sensor is an RTD? Is there a general resistance range these run in or does it vary by manufacturer? I would think they would have to be same so they can work with various manufacturers AquaStats.



Is there any documentation on testing/debugging the AquaStats? I'm guessing a relay is stuck but I'd like to verify that before I buy a new AquaStat. I don't mind replacing parts, I just want to make sure I replace the right one(s).



Also, thank you for your help, it's greatly appreciated.

Steamhead

You probably need a new aquastat

which won't come cheap. On these units the temp sensor is integral to the control. Best bet in that case is to HAVE A PRO replace that all-in-one aquastat/primary control with separate, updated components. In particular, this will allow the use of an updated oil primary with a 15-second trial for ignition- the R8182 units have a 45-second trial which is considered way too long nowadays.



I believe the V-14A series came with Carlin burners- Carlin makes a 15-second primary for their units.