Shorter heating cycle after domestic coil replacement

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Old 01-05-13, 05:45 AM
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Shorter heating cycle after domestic coil replacement

Hi all, first post.

We have a Weil McClain oil furnace with baseboard hot water and 3 hydronic toe kick units. We had the domestic coil replaced recently as it was corroded and flaking rust.

After this was done our heating cycles are a little closer together - used to be every 30 - 32 minutes heat would fire up, now around 23 - 26 minutes (same average temps outside).

Also notice two other things:

1) Circulating pump comes on and runs roughly 40 seconds before the burner does. These two used to come on together. We had the same behavior 2 years ago when there were issues with the original install and air in the system.

2) The basement is warmer than it was before the repair, which leads me to believe that less heat is going upstairs than before.

I was right there watching the service tech remove and reinstall the coil. It went (thankfully) uneventful. The system was purged of air after the install and there are no telltale signs of air in the system.

Other than the coil, nothing has changed in the system. The one thing that the tech did do was adjust the pressure of the auto water feed valve, so maybe that has something to do with the new behavior?

TIA,
JP
 
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Old 01-05-13, 07:43 AM
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Sounds odd to me.

What is the model # of the boiler?

What are the settings in the aquastat? Hi/Lo/Diff?

What does the pressure and temp say on the boiler gauge?

Once we get that info we can move forward.....
 
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Old 01-05-13, 02:30 PM
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Weil McClain P-368-WT

Hi - 180
Lo - 150
Diff - 15

Pressure roughly 18 PSI
 
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Old 01-06-13, 01:54 PM
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Forgot to add, temp on gauge shows around 200 degrees after running
 
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Old 01-06-13, 04:15 PM
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After this was done our heating cycles are a little closer together - used to be every 30 - 32 minutes heat would fire up, now around 23 - 26 minutes (same average temps outside).
I can think of no possible way that anything that was done to the boiler would cause the thermostat to call for heat more often. There would be no relationship between a thermostat calling for heat and changing the coil in the boiler. No, not even changing the pressure in the system. Thermostat calls when it needs heat... and that's it.

1) Circulating pump comes on and runs roughly 40 seconds before the burner does. These two used to come on together. We had the same behavior 2 years ago when there were issues with the original install and air in the system.
Did you happen to note the TEMPERATURE of the boiler when you noticed this behavior? If the boiler was above the high limit temperature, this is normal behavior. The burner will not fire until it is 10 below it's high limit setpoint. If the boiler was at say 190 and the heat call arrived, the pump alone would turn on and run. The boiler would then cool somewhat and the burner would fire.

2) The basement is warmer than it was before the repair, which leads me to believe that less heat is going upstairs than before.
Don't mean to be rude or anything, but this could well be your imagination playing tricks on you... but if the thermostat is calling for heat more often, and the boiler is firing more often, the basement will be warmer... so maybe it's that.

Pressure roughly 18 PSI
This is when the boiler is HOT, correct?
 
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Old 01-06-13, 04:21 PM
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temp on gauge shows around 200 degrees after running
This is after the heat call ends and the pump is no longer running, correct?

Again, probably normal.

If there is a heat call and the boiler fires up to say 180 and the heat call ends, the burner will shut down and so will the pump.

With no further circulation in the system the heat that is in the cast iron of the boiler will then soak into the water and raise the temperature above the setpoint...

Normal behavior.

If on the other hand the burner does not shut off at 180 setpoint WHILE A HEAT CALL IS IN PROGRESS, then there may be an inaccuracy in the aquastat...

Wait for the boiler to cool down ... shut it off for an hour or two if you have to. Push the thermostat up to force a long heat call. Observe the temperature that the burner shuts down. It should be within 5-10 degrees of the setpoint.

Turn the thermostat back down again and observe the temperature in the boiler rising due to the 'heat soak' occurring after both the burner and the circulator shut off.

Let us know if you see different behavior.
 
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