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Cause of Peerless MI-03 Lockouts
New Peerless MI-03 Boiler installed four months ago. Had two lockouts, one two months ago, the other a week ago. First thought in May was defective damper; not the case. Hitting re-set button solved it in both cases. Opinion then was that some kind of blocked vent switch/downdraft caused it, thunderstorm etc. But this past week air weather was calm.
I have heard that low system pressure can cause such a lockout. Installer says he set expansion tank pressure at 18psi and I see the autofeed prv is set to about 16. Should they be set the same? I measured a system height of 16ft above the expansion tank which the Westank calc said based on that the initial pressure should be set at 17. So those settings seem to be ok. (We have an older house, ceiling heights are a little higher.) On initial install pressure gauge at PRV read about 15-16.
Around the time of the first lockout (not sure if before or after) I noticed pressure gauge was up to about 20-22. (Total system water around 70 gallons, including 48 for Turbomax). I let a little water out of the boiler and it returned to 15 about 6 weeks ago. Right after the most recent lockout, I noticed pressure was back up to about 20. What does this sound like? System controller is Hydrostat 3200+. Set to cold start.
Manual indicates possible causes: defective gas valve, plugged orifice spuds, gas off, flame rollout switch open, limit not working, etc. some of these-- like orifice spuds-- require cleaning.