Boiler coming on when not needed...?


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Old 02-02-14, 07:38 AM
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Boiler coming on when not needed...?

We have a house from the 1950s with an oil fired furnace heating water for radiators. There are 2 zones, the kitchen on its own (a single electric blower radiator) and the rest of the house, and there are 2 thermostats, a simple mercury one in the kitchen and a White Rodgers electronic one for the rest of the house. The boiler has a 'TACO' tankless water heater on the side, but the wiring to the attached control (a thermostat) has been cut off (at least 25 years ago), and while the copper pipework is still all there, we have a regular electric water heater.

Due to the cost of oil, we have been using the furnace sparingly, and I have recently got it working well again after a couple of years non use. This morning, with the White Rodgers thermostat set to OFF and the Kitchen thermostat turned all the way down (well below the temp in the kitchen), the boiler was running this morning when I woke up. I don't know how long it would have run - I flipped the breaker to cut if off.

What is causing the boiler to fire when neither thermostats are calling for heat???

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Old 02-02-14, 07:45 AM
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Hello and welcome....

It would seem to be a t stat issue IMO...

But can you take a pic of any and all controls of the boiler?

Aquastat, relays by the pumps, zone valves and such???
 
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Old 02-02-14, 07:47 AM
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It may be in your best interest to replace that dinosaur before next winter and not throw too much money at it...( if any at all)

And when the boiler runs do you get heat from any one of the two zones?
 
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Old 02-02-14, 07:56 AM
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When the boiler runs are you getting heat or is running to maintain temp.
Although the aquastat wire was cut your boiler control may still be set up for warm start boiler.
What do have for boiler control and what are the settings. You should have high & low knobs.
For now turn low down as far as it will go or shut the switch off until you need the heat.
 
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Old 02-02-14, 08:14 AM
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I like my dinosaur!

When the furnace is running 'normally', it heats very well, in both zones, and the thermostats control it as you would expect. About 15 years ago when we re-did the kitchen, they put the kitchen in its own zone (gets cold in there) - I think they redid all the controls then (professional installers).

There are 2 Honeywell R845A's on the wall by the boiler connected to the thermostats. There is a Honeywell L8124G Triple Aquastat Relay. I can take pics if it will help.

I seem to remember the furnace would run periodically by itself for short periods in the past - didn't worry about it when oil was 85 cents.

Its not really a super big problem, just curious why its coming on 'by itself'.
 
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Old 02-02-14, 08:21 AM
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Wait for Trooper to come on later... He is a moderator and will suggest how to modify the control to make it cold start so it does not fire to keep the boiler warm... Its very simple...
 
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Old 02-02-14, 08:31 AM
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It's coming on to maintain the low limit on your L8124 just as though you were still getting your hot from the boiler.
If you open up your control and lower your low limit to the lowest it goes that's the temp it will maintain.
You can make it a cold start control but personally in your case I wouldn't do it. I'm sure others will disagree but with the large amt of water in the boiler, to try and heat it from scratch every time I think will cost you more than the couple of minutes it runs to maintain temp, not to mention the comfort level while you wait for it to come up to temp. I don't think it's worth it.

If you want to save a little money just turn the low limit down a little to where you're comfortable.
 
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Old 02-02-14, 09:18 AM
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OK THANKS! (light bulb comes on). So, essentially, the low limit on the aquastat sets the temperature that the furnace maintains *within the boiler* at all times, making the furnace come on for short periods even when the thermostats are not calling for heat. I just tuned the low limit control way down below what it was set to (was 160) and heard the relay click. This will let the boiler go cold and stay cold I presume. I'd actualy prefer this, we have a heat pump when its not too cold, and would really want to run the furnace for periods when it gets really cold, so cold starting is not a problem I think. The burner on this unit has a 1.5 gph nozzle, so it can get through a significant amount of oil in a pretty short time - I'd prefer to use it for heating and not maintaining the boiler temp when we're really not using it (I'm in VA, so its not really cold all the time here).

We also have a wood fired furnace hooked into this system, I have some q's about that also, but I'll start a new thread for that.
 
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Old 02-02-14, 12:54 PM
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mshedden,
That's exactly right. You will fine running that way.
That 1.5 gph can do some damage.
 
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Old 02-02-14, 02:02 PM
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You can make it a cold start control but personally in your case I wouldn't do it. I'm sure others will disagree
I'm not gonna disagree with Spott on this one...

I just tuned the low limit control way down below what it was set to (was 160) and heard the relay click. This will let the boiler go cold and stay cold I presume.
"Stay cold" ... as in not fire up at all? No... it will still fire up but maintain a lower temperature when there is no call for heat.

I believe I would use a LOW setting of 130, and a DIFF of at least 15.
 

Last edited by NJT; 02-02-14 at 04:39 PM.
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Old 02-02-14, 04:29 PM
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If the burner does not stay on long enough to raise boiler water temperature above 130f the heat exchanger may have condensation on it which is bad. I would make it cold start by removing the blue wire on the control.
 
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Old 02-02-14, 04:35 PM
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I would make it cold start by removing the blue wire on the control.
Not a good idea with THIS boiler.

First, there's more to it than just 'removing the blue wire' because all that will do is inhibit the burner on low limit and does nothing for circulator control.

Second, with a big old boiler like that it doesn't make sense to cold start it with the massive amount of water it contains. Thermostat would call and it would take FOREVER to reheat the mass of water in the boiler. It's kinda like doing super steep setback on thermostat... you would lose by having to reheat all that water every time what you might save by just keeping it warm in between.

Not only that, but it's going to condense a LOT LONGER during the time it takes to bring the boiler up from cold.

If the boiler fires up at 130 on low limit, there is no circulation, and no condensation, because the boiler is already at 130 and there's no circulation on low limit firing.
 
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Old 02-02-14, 04:49 PM
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I have used removing the blue wire many times to go cold start and the burner stay off until there is a call for heat TT and then the burner fires and pump stays off until low limit setting is reached and then begins to deliver heat to house . The boiler is fired at 1.5 gal. so should not take too long. If it does not maintain comfort put wire back on , just another option that has worked for me.
 
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Old 02-02-14, 05:13 PM
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I know what the 'blue wire' does.

What I'm saying is that does not address the circulator operation. The circ is still under control of the low limit.

It's a BIG boiler, there's like 30 gallons at LEAST of water in that boiler. Even at 1.5 GPH it's gonna take a while... and it's going to condense the whole time it's coming back up to temperature.
 
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Old 02-02-14, 05:20 PM
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That's all true it will condense on its way back up , but as long as the burner stays on long enough to dry out the heat exchanger all is good.
 
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Old 02-02-14, 06:17 PM
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But it probably won't save any money by cold starting...

So what's the point of cold starting?

There isn't one.
 
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Old 02-02-14, 06:35 PM
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Stay focused gentleman please...
 
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Old 02-03-14, 06:14 AM
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I have to respectively disagree with Trooper on cold start boiler operation saving fuel.
 
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Old 02-03-14, 06:58 AM
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That's nice... you are entitled... but I think you meant "... respectfully..." ?

I never once made a 'blanket' statement that cold starting does not save fuel. I clearly stated that with THIS PARTICULAR BOILER it does NOT make sense. There is nothing to be gained from it in THIS PARTICULAR instance.

Posts are going to start getting deleted because this has nothing at all to do with helping the problem or question at hand.

If you wish to further discuss the merits or demerits of cold starting a huge old boiler with 30 plus gallons of water in it, start a new thread. Do NOT continue to argue the point here in this thread.

This is the last I'm going to argue...
 
 

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