Boiler Overheating

[axman977]

Hi everyone,
I am new to the site and rather new to the wood boilers. I own a tree care company so wood is of no issue to me and when I bought my house a year and a half ago, I knew I wanted a wood boiler in my barn feeding the house. I bought a Thermo Control 2000, installed myself with about 110' of Pex Flex pipe to the house. Last season the unit worked flawless and I burned all summer long just for domestic hot water. I am basically propane free now and LOVE IT. Back around Thanksgiving, I had a problem with the boiler and it took me a couple weeks to narrow down what the problem was. I woke up to the pex flex burst open and flowing water all over. Luckily in this particular spot it was not very deep and I was able to make a quick repair. Not knowing what had happen I fired the boiler back up and low and behold it did it the next night, then a few nights later etc, etc. Finally on Thanksgiving day, I was home all day when it had happened again, this time I caught it. The automatic damper on the door of the boiler was sticking open, causing the boiler to overheat, melt the pex and blow the pipe. Needless to say I was not happy. The folks at Thermo Control have been great and are hooking me up with a repair length of Pex Flex.

My question is this. Thermo Control recommended I install a strap on aquastat inside the house to kick the blower fan on should the temp of the boiler ever exceed say 190 or so. I have a Honeywell L6006C and I have tied it using the R and W wires to the red and white wires on my fan relay. The problem is that for some reason I cannot figure out the aquastat will randomly turn the blower on when the water is well below even the highest setting of 200 degrees. Why would it do that? The other question is will this aquastat turn the blower back off when the water temp is below whatever the setting is? What am I missing? Any help would be greatly appreciated.

Luke

 

[Clarkbug]

My question is this. Thermo Control recommended I install a strap on aquastat inside the house to kick the blower fan on should the temp of the boiler ever exceed say 190 or so. I have a Honeywell L6006C and I have tied it using the R and W wires to the red and white wires on my fan relay. The problem is that for some reason I cannot figure out the aquastat will randomly turn the blower on when the water is well below even the highest setting of 200 degrees. Why would it do that? The other question is will this aquastat turn the blower back off when the water temp is below whatever the setting is? What am I missing? Any help would be greatly appreciated.

Luke

First, welcome to Hearth!

Next, I would fix the sticking controller on your boiler first before you do anything else. Having a heat dump is a good idea, but shouldn't be used to fix another problem.

You might also want to add a T&P relief to the boiler so that blows before your pex does....

Sounds like you have the aquastat terminals right. Is it directly on your piping? No insulation, good direct contact? If so, check your relay, might be something wonky there.

And yep, it will turn the fan off once the water cools below the differential that you set in the aquastat.

 

[axman977]

Clarkbug,
Thanks for writing back. I should have included in the original post that I had found and fixed the issue with the sticking damper on Thanksgiving Day. That was why Thermo Control ultimately agreed to replace the pipe.

I wasn't aware of a T & P relief, there is a pressure relief on the unit already but I'll have to research the temperature ones. Would that be the simplest fix? Could I ignore a heat dump system if I did a T & P relief?

The aquastat is direct on a portion of copper pipe, no insulation. I'm wondering if maybe I have a faulty aquastat? The relay appears to be working fine because everything works as it should with thermostat controls and what not. Maybe I should call Honeywell?

Thanks!

Luke

 

[Clarkbug]

Clarkbug,
Thanks for writing back. I should have included in the original post that I had found and fixed the issue with the sticking damper on Thanksgiving Day. That was why Thermo Control ultimately agreed to replace the pipe.

I wasn't aware of a T & P relief, there is a pressure relief on the unit already but I'll have to research the temperature ones. Would that be the simplest fix? Could I ignore a heat dump system if I did a T & P relief?

The aquastat is direct on a portion of copper pipe, no insulation. I'm wondering if maybe I have a faulty aquastat? The relay appears to be working fine because everything works as it should with thermostat controls and what not. Maybe I should call Honeywell?

Thanks!

Luke

Glad the damper is fixed!

Yup, a T&P is like the one on your domestic hot water heater. Will blow if either exceeds the limit, but not sure what the standard settings are out there.

I would not suggest using that instead of the dump zone. The reason being you could have a problem and be dumping water all day without knowing. With the dump zone your house gets hot and you know you have a problem. Plus it prevents your boiler from dry firing and maybe damaging itself.

Check the aqua stat before you call anyone. Disconnect your fan wires first. If you can, measure the temp of the pipe. Then rotate the dial until the setting is near the pipe temp. It should then have continuity between the terminals. Turn it back up and it should go open. If it does those things, its a problem with the wiring to the relay, not the aquastat.

 

[Boiler Installer]

Hi Luke,

I am wondering what the actual water temp was when you say it overheated. Did you notice a blowoff at the rear of the boiler? What is the highest you have ever seen the water temp get to at the boiler?

The L6006C has two terminals on it if I am not mistaken. You should run those wires back to your main controller just like it was a thermostat. I am not sure what the wires on the back of the relay are, sounds like you think that is where the relay is tripped. Isn't there a place where the other thermostats connect? You should use that aquastat just like any other thermostat. That aqustat also has a 30 deg differential. If you have it set at 30deg. it will vary the temperature above and below the set point by 30deg. You should just take a look at it and set it to some number that is tight like 10deg. It is a little white wheel that sets back on the right side as you are looking at the aquastat from the front. (cover removed)The wiring on your aquastat is suspect and it should work very
consistently every time for a long time.

Another thought I had was what line is the aquastat mounted on feed or return? It should be on the feed side from the top of the boiler going into the house.

Another thought I had was if you are running with a 30lb blowoff which everyone is, you should have exceeded that pressure before the water got hot enough to melt the pipe. The pipe is usually rated for 210 and can handle some more. Maybe it blew off and then melted the pipe. The boiler is in the barn so you may not notice it before the meltdown.

If you start the boiler from cold, you should have to relieve the pressure in the system at least once and more likely twice going from 55 deg water to 180 deg water. If you don't get the pressure lowered at higher temps you could be going back and forth with this (blowing off/melting pipe). I say heat the water in the stove up to 180 and let some water out of the drain valve at the bottom of the stove until the pressure lowers down to about 15 lbs. (Make sure you are looking at lbs and not bars on the pressure gage) Your automatic fresh water fill valve is usually factory set to 12.5 lbs pressure (you do have an automatic fill valve with backflow preventer?)

Another thought is what size expansion tank are you using. I would hope you are using at least a #60 but I prefer a #90. You should check the tank to see if it is still holding pressure in the bladder. There is a shrader valve on the tip of the expansion tank and you can push in the valve very quickly and listen for air or see water come out. If the air comes out the tank is still good. If you get ANY water you will need a new tank.

I don't think a T & P valve is a good idea. They put them in hot water heaters at 210 deg limit with 150lb pressure. Those type of heaters are not like wood and with wood you can and sometimes do get overheat temps. Who wants a blow off if the water temp gets too high? The pressure valve corrects itself very quickly and usually stops flowing water very quickly. The temp valve could run water for a long time causing water to leave the boiler faster than the automatic fill valve can fill causing an even worse overheat condition by lack of water in a runaway stove.

There is nothing worse than having a stuck open air door in the wood burning business. I think it is very rare to have that happen. Those type of controls are usually made by Honeywell or Erie and they have been making the same old models for ever. Maybe it was a defect in the mechanical flap on Thermo Controls end, but I think it is very rare. You should have a good large expansion tank and a tested overheat protection system. I wonder what the water temp was when the pex tubing melted. That would be the question of the day.

I hope some of this helps. I'm sure some may sound obvious to you but not to all......believe me.......

 

[brant2000]

I control mine from overheating with a very cheap controller I bought on ebay, like this (broken link removed to http://www.ebay.com/itm/DC12V-Digital-LCD-Aquarium-Fish-Tank-Thermostat-Temperature-Regulator-Controller-/301142785779?pt=LH_DefaultDomain_0&hash=item461d823ef3). I have used other controllers to do this also, but swapped those out for other uses since this simple control was all that's really necessary. It works very well, because although it's in Celsius and not calibrated well, I can easily adjust the set point temperature and it uses a preset 5 deg C offset, meaning that it kicks the blower on at about 200 F and off at about 185ish F. This acts as a simple relay that is installed in parallel with the fan contacts on the blower, which turns the blower on as long as the relay is closed.