Honeywell ra832a issues?


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Old 04-10-15, 08:22 PM
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Angry Honeywell ra832a issues?

Howdy. Just as the winter is ramping down to its final stages in NJ, I'm finding myself with a thermostat/control issue. Please bear with my explanation below and kindly advise your thoughts. I appreciate any guidance or insight I can get!

Background: I have a 3-zone hot water heating system with baseboards. 3 low voltage thermostats; 3 honeywell ra832a switching relays.

Issue: The circulation pump and thus the HW flow and heat to one of the three zones does not shut off when the thermostat wants to shut it off. This happens 80-95% of the time and it runs indefinitely thereafter. It also happens to be one of the lower level zones, responsible for one of the least used areas of the house. There have been times last week that I've woken up in the morning to find it ~80 degrees on the upper level (!) as a result of constant system on.

Diagnostic efforts: I've done some initial work and found that when it's stuck like this the only way to shut it off (aside from main boiler switch) is to disconnect the wiring between the thermostat and the honeywell ra832a. There is no short on the wire between thermostat and honeywell ra832a and the relay does click off on the thermostat, so that's eliminated as a cause.

Questions:
(1) Is this a stuck relay in the honeywell ra832a?
(2) Why do all three of the honeywell ra832a read 15.5v between the T terminals when it's supposed to be 24v? (strange but thinking unrelated as the other 2 zones are working fine?)
 
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Old 04-11-15, 06:18 AM
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What type of Tstat? Can you swap a Tsat from another zone and see what happens?
Sure sounds like a stat problem.
Geo
 
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Old 04-11-15, 11:08 PM
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slavkala.... I moved your post to the boiler section as this might be a little more involved than a thermostat.

Do you have three zone valves or three circulator pumps in your system ?
 
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Old 04-12-15, 05:38 AM
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If undoing the wire from the thermostat shuts it down it is either the wire or the thermostat. If you can pull the thermostat and it it shuts down it is the thermostat. If it was a wire it would continue to run after the thermostat is pulled.
 
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Old 04-12-15, 09:07 AM
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Let me expand on the diagnostics a bit.

If you disconnect the t'stat wires AT THE 832 RELAY and it shuts off, then the problem is the thermostat or the wiring.

You can further determine which is which by leaving the wires on the relay and disconnecting AT THE THERMOSTAT. In this way you can isolate to either the wire OR the thermostat.

There is no short on the wire between thermostat and honeywell ra832a
How do you know this?

the relay does click off on the thermostat, so that's eliminated as a cause.
Not necessarily. The contacts on a relay can stick closed even if you hear it click.

Why do all three of the honeywell ra832a read 15.5v between the T terminals when it's supposed to be 24v?
I would first suspect that there's an issue with your meter device. What make/model are you using? Is it analog or digital? Have you measured the 120VAC supply to the relay?
 
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Old 04-14-15, 07:11 PM
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Thank you all for your feedback! It's much appreciated. I did solve the problem, but want to summarize:

Meter is a Fluke 77 and I have extensive experience with electronics (custom building hi-fi and tube amps for 13+ years now), so no short was detected when measuring resistance between the two tstat leads. Ended up measuring current flow on the wiring when the issue occurs, and after some finagling found that the leads short intermittently somewhere along the run (seems like a paradox as the wiring isn't more than 25 years old and insulation is perfect where visible). My conclusion is that this happens when the wiring heats up ever so slightly from current flow - confirmed by measuring resistance and finding dead short when in operation and disconnected from tstat. However, after waiting 10 minutes and allowing leads to cool down the short disappears!

The only trailing question is the 15.5v. Meter is not at fault and there's a solid 120vac on the opposite side of the transformer, so this one has me a bit stumped... But I suppose it's immaterial at this point as function has been restored.
 
 

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