Oil Boiler Turning on whenever there's a call for heat???

NewBoiler said:

My wood boiler is all connected and working great. However, I have a problem with my oil boiler. I originally thought that as long as my oil boiler is up to temp (from my wood boiler), the burner would never turn on. What I am finding is that even when the oil boiler is up to temp, and a zone valve asks for heat, the burner turns on in the oil boiler.

I have read that you can setup a relay on the oil burner to shut it off when the wood boiler circulator is running, but I can't find a post about this. Do only some oil boiler burners do this? A friend's oil boiler burner only kicks in when the temp in the boiler is below the aquastat low limit.

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Probably you've got a dual-aquastat control with a both a low-limit and a high-limit aquastat, possibly a Honeywell L8124A.

When there is a call for heat the low-limit aquastat is bypassed and the high-limit aquastat takes over. This way the boiler maintains a minimum temperature range while on standby waiting for a call for heat, but then goes to a higher range for as long as there remains any demand for heat. Also the circulator is disabled when the boiler temperature drops below the bottom of the low-limit range and is reactivated when the boiler temperature rises above the top of the low-limit range.

Have a look at the installation guide for your aquastat; review your oil boiler specs; consult with a qualified HVAC professional; and see if you can adjust your low-limit range down to maybe 140-150 degF and your high-limit range down until the top of the high-limit range is below the minimum temperature you expect from the wood boiler, maybe 155-165 degF, 150-160 degF, or even 145-155 degF if necessary.

Cheers --ewd

I put up with the same thing the first year. Now I unplug the burner.

NewBoiler said:

Thank You. Yes , it is actually a Honeywell L8124L aquastat. So if this aquastat was a triple, it wouldn't have this issue?

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L8124L, L8124A, same idea, it should be possible to make it do what you want with range adjustments, once you understand how it works. Print out a couple copies of the schematic and trace what's hot and what's not with colored pencils according to the state of the inputs, the temperatures rising and falling, and so forth. To me they're very confusing but I think I finally got a handle on it once I got the crayons out.

I don't know what 'triple aquastat' means, although they say that's what an L8124 is. There's two aquastats, three aquastat contacts, one relay, two relay poles, a cirulator output, a burner output, and a call-for-heat input. I have no idea what the triple refers to.

Cheers --ewd

Get yourself an aquastat that opens on temperature rise, and install it into the supply from your wood boiler, or you can use tha strap-on style and attach it to the supply from the wood boiler. Run a pair of wires(18-2 tstat cable would be great) from the two contacts on the aquastat to the T & T contacts on the oil burner ( they are probably jumpered ) set the aquastat to 140 or so and as long as your wood boiler is supplying water above the set point your oil burner won't fire. When the temp drops the oil will kick on AUTOMATICALLY.

[I actually have it unplugged now too, but would like to have it as an 'automatic' backupas in if the wood boiler goes out when I'm not home, the oil boiler will kick in. With the burner unplugged, it will never kick in.[/quote]

The line that you have "unplugged". Connect it to the power source through a relay that is controlled by something on the wood boiler - like an aquastat. When the water in the WB is hot, the relay is off-no power to OB. When the WB water cools off the relay connects and you have power to the OB. Simple but I think it gets you what you want.

You'll need a relay, aquastat or temp sensor, and a 24v. source (transformer or existing source)

It's also possible to have the relay controlled by something else, such as when the power is on to your WB fan.

NewBoiler said:

I actually have it unplugged now too, but would like to have it as an 'automatic' backup as in if the wood boiler goes out when I'm not home, the oil boiler will kick in. With the burner unplugged, it will never kick in.

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Run this past your local technician and see if he has any reservations:

Write down where each of the three adjustments is currently pointing.

Turn the low-limit differential knob clockwise to 10 degF.

Turn the low-limit setpoint to 150 degF.

Turn the high-limit setpoint to 155 degF.


--ewd