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Old 03-06-2010, 07:40 PM   #46
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Need help with heat and hot water issue


What temp and differential is teh pipe mounted aquastat set to.

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Old 03-07-2010, 03:34 AM   #47
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Need help with heat and hot water issue


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With radiant heat, there is virtually no reason to have the boiler set to 180 low and 200 high on the limits. Its a waste of fuel.

With a dual aquastat. The boiler temp is maintained by the low limit.

The short cycling you describe, could be a problem with the limit, or a loose connection it it, or else where. Or, the aquastat on the pipe could be cycling it.

Normal operation would be.

Standby temp maintained at low limit setting, varying only by the temp differential of the aquastat.
On a call for heat, burner runs until either the boiler temp reaches high limit setting or thermostat stops calling for heat. As long as there is a call for heat, the burner cycles on and off by the high limits 10 fixed differential.
Once the call for heat is satisfied, the boiler goes back to standby operation.


You said it doesn't reach set temp. Are you referring to 30C again? A radiant system may not be able to reach that temp except on the mildest of days.
And on normal cooling days, trying to reach it, even if it can do it, will takes many hours.

To check boiler temp rise, you can use a regular contact thermometer. Place insulation around the area your using to check temp, and insert thermometer in between insulation and pipe. repeat t opposite pipe.

On your system, the low limit should be no higher then 140.
So maybe the system is working correctly except the settings maybe wrong. So what should I set the lo and high limit to on the boiler aquastat? It's currently set at 200F hi and 180F Lo. Theres no differential setting so it must be a fixed differential. I never changed the setting on the boiler aquastat it was at 200F hi and 180F lo before I even did anything.

But why would the boiler temp drop down to 140-150ish mark? Shouldn't it stay at 180F mark if the Lo limut is set to 180F?
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Old 03-07-2010, 03:37 AM   #48
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What temp and differential is teh pipe mounted aquastat set to.
It's a single function aquastat set to 180F. It doesn't have a differential setting on it so it must be fixed also. I don't know what the fixed differential is on it.
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Old 03-07-2010, 04:00 AM   #49
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It's a single function aquastat set to 180F. It doesn't have a differential setting on it so it must be fixed also. I don't know what the fixed differential is on it.
Should be marked on it somewhere. But could be unreadable by now.

On your double aquastat. I would set the low to 140, and the high to 180.
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Old 03-07-2010, 07:28 PM   #50
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Should be marked on it somewhere. But could be unreadable by now.

On your double aquastat. I would set the low to 140, and the high to 180.
Ok, I've set the double aquastat high to 180 and low to 140. Should I leave the single function aquastat at 180?

I guess I'll leave the heating system as is for now. The house is warm and there is hot water.

Thanks for all your help Beenthere. Much appreciated!!!
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Old 03-07-2010, 08:46 PM   #51
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Need help with heat and hot water issue


The single aquastat on the pipe. Is generally used for a safety high limit.

Leave it at 180.

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