Hot water heat stays on constantly, does not respond to thermostat set point.


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Old 03-11-14, 06:51 AM
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Hot water heat stays on constantly, does not respond to thermostat set point.

I have two zone hot water heating, natural gas boiler Crown Aruba Model DG75 EI, serial number 31586 with two new Honeywell 5-2 thermostats and an Aquastat Relay L8148E.

System will demand heat, sometimes on one of the two zones, sometimes on the other, sometimes on both and fail to cease supply of hot water once set temperature has been reached. House becomes like a sauna.

Did resolve the issue for about two weeks by turning the entire system off and leaving over night for zones to cool below set point (60 F each zone). Then powered up again. Worked normally for two weeks. Then constant heat returned.

Replaced both thermostats with brand new Honeywell 5-2. Constant heat. Turned system off to cool zones below set point and turned back on. Constant heat.

Might problem be with the Aquistat Relay L8148E? How to troubleshoot?

Any suggestions gratefully received.
 
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Old 03-11-14, 07:03 AM
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Chances are you have a zone valve failing in the open position. Do both zones remain hot or is only one zone causing the problem?
 
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Old 03-11-14, 07:20 AM
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Do you own and know how to use a multimeter?
 
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Old 03-11-14, 07:27 AM
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NJ Trooper: Yes, have and can use a multi meter.

tomf63: problem has manifested itself in different ways under different conditions - some instances are zone 1 only open - others are zone 2 only open - again with both 1 and 2 open - each instance after turning system off and then back on again etc.
 
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Old 03-11-14, 07:36 AM
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Might problem be with the Aquistat Relay L8148E? How to troubleshoot?
Might be... I think first thing to do is determine if problem is with zone valves and wiring, or with aquastat.

You can do this by monitoring the voltage at the T T terminals of the 8148.

If the zone valves are calling for heat, you will see ZERO volts at the T T terminals.

If there is NO call for heat you will measure 24 VAC (nominal) at the T T terminals.

So, if there are NO calls for heat from the thermostats, and the zone valves 'should be' closed, and the 'endswitches' in the zone valves open, you shoul be reading 24 VAC at T T .

If you find that the 8148 is still producing heat... and the circulator pump running... with 24 VAC at the T T terminals, then the problem would seem to be in the aquastat. 'Stuck' relay possibly.

If you find that you have ZERO volts at the T T when you should not, then it means that the problem is 'upstream', either in the wiring, the zone valve endswitches, or possibly the thermostat.

What type of zone valves do you have?
 
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Old 03-11-14, 10:07 AM
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NJ Trooper: Thanks for those hints. I am not sure how to respond to your query " what type of zone valves do you have"?
 
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Old 03-11-14, 12:02 PM
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I am not sure how to respond to your query " what type of zone valves do you have"?
Make and model of the electric zone valves... Honeywell? Taco? Erie? White-Rogers? etc... and the model
 
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Old 03-11-14, 12:18 PM
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Will check into that when I get home and provide information then. Thanks.
 
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Old 03-11-14, 12:35 PM
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Once I know that I can provide a few further checks you can do with the multimeter.
 
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Old 03-12-14, 11:24 AM
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The zone valves are Honeywell V8043E.
 
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Old 03-12-14, 12:28 PM
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Have you had a chance to check the T T yet?

I'll wait with the further checks until you get to that point because further testing course might change when we know.
 
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Old 03-12-14, 01:11 PM
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TT reads 0 V as it should, when heat is called for by thermostat. This appears to indicate that the Aquastat is working.
 
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Old 03-12-14, 01:31 PM
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TT reads 0 V as it should, when heat is called for by thermostat
OK, but on the other side of the coin... you need to look at it from both directions to rule out anything.

When NO HEAT is being called, does it ALWAYS read 24 VAC?

Do the burners continue to fire and the circulator pump continues to run even when the T T reads 24 VAC (no heat call)?
 
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Old 03-12-14, 02:49 PM
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It will take me a while to nurse the system and obtain valid answers to those questions.
 
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Old 03-17-14, 06:23 AM
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Thanks, got it sorted. The zone valve was sticking, armature not sprung.
 
 

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