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Honeywell 7800 help

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carlta
carlta Member Posts: 2
in Gas Heating
Alright, I'm stuck. (Full disclosure: I'm barely a mechanic, let alone an burner specialist. I just happened to read the manual for our oven and inherited this equipment when our maintenance man retired)
Here's the issue. We have a honeywell RM7800 relay hooked up to a gas burner that heats kiln ovens. We recently expanded the plant and moved the unit and ever since the move, the relay will randomly enter standby mode mid-cycle every now and then (it works fine 80% of the time, but seems to glitch a couple times a week). No error code, no alarm, just switches itself from run to standby and has to be reset to recycle. I had a contractor in and he couldn't figure it out. Hoping someone else out there has experienced this before or has some tips on what to check.

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  • JStar
    JStar Member Posts: 2,752
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    Sounds like it's losing the run signal. Is there an operting thermostat in the oven? The contacts or wiring may be glitchy.
  • JUGHNE
    JUGHNE Member Posts: 11,061
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    You are almost to the head of the class as "you read the book", probably ahead of the contractor you called in. ;)

    Wiggle, shake and bump to find the bad connection somewhere.
    I use a all plastic sharpie pen as a "probe". It is all insulated and you can push hot wires around fairly safely with it.
  • carlta
    carlta Member Posts: 2
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    Thanks! There is a thermocouple in the oven, I'll check the connection tomorrow. But the log on the PID controller that runs the oven matches the loggers I put in the oven and is also set to lockout and alarm if the signal from the thermocouple is absent.
    When it errored a yesterday, I was closest to the gas pressure switches and reset them second in the sequence after the relay reset(i normally reset them last, after resetting controllers), and the burner fired after this (without a controller reset). gas pressure on the gauges are in spec, so I'm wondering whether there could maybe be an issue with the pressure values that could cause an error such as this?
  • Steamhead
    Steamhead Member Posts: 16,835
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    Might be one of those pressure switches- ISTR they are wired into the same control circuit as the other limit controls. If the gas pressure is within spec, one of the switches is bad.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • gennady
    gennady Member Posts: 839
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    If you need to reset it to start, then it is not a control circuit issue.
    If it stops mid cycle, it might be loss of flame during run or other reasons.
    Gas pressure switches have their own resets. Resetting only controller will not restart system. So, if you reset control and system starts , then it is not gas pressure switches.

    if you would have display module installed, it will give you error code and also it has error history.
    Gennady Tsakh
    Absolute Mechanical Co. Inc.
  • JStar
    JStar Member Posts: 2,752
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    A loss of flame should give an alarm during any time from ignition to main flame. Reverting to standby is usually triggered by a loss of run-demand. I would start tracing control wires. Can you upload the oven manual, or post the model number?

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