Weil McClain boiler

Old 11-29-05, 08:37 AM
Ross Bentz
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Weil McClain boiler

I've got a Weil McClain hot water system in my house...circa 1986...over the past couple weeks, I've found that the boiler cycles off and then never comes back on regardless of the thermostats. I have 3 zones plus a hot water tank with a thermostat and none of them seem to be turning the boiler back on. We woke and found the house in the low 50s the other day. I tried turning up each of the thermostas but the oil burner did not fire. I manually depressed the relay in the Aquastat and the boiler fired up and ran fine for the rest of the day. It reaches the correct temperatures in each of the zones and then shuts off. I make my living troubleshooting electrical circuits and I've done some work on industrial boiler systems but I'm looking for a little insight into the intricacies of this type of boiler. Any suggestions are greatly appreciated.
Old 11-29-05, 10:29 AM
Ross Bentz
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So I was thinking about the aquastat and its function...the low temp is set at 120 and the high temp is set at 190...my expectation is that when the system is turned on, the boiler should maintain a temperature between these two points...then, when a thermostat calls for heat, a circulating pump should switch on and send hot water to the zone in need...cooler returning water should force the boiler to continue heating and maintain the temp dictated by the aquastat...

In my system, however, I find that the boiler temp goes all the way down to room temperature and the aquastat never turns on the burner until I manually push the relay...my thought is that the aquastat is bad or some component of it...unless, of course, my system is not set up to "maintain"
Old 11-29-05, 03:31 PM
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If your system was not set to maintain temperature in the boiler, the burner should fire upon a call for heat from a thermostat. The fact the safety circuit is locking out, tells me the burner is getting a signal to fire at some point in time. As a test, with the boiler at rest, turn up the thermostat. The burner relay should pull in. You can simulate a call by jumpering terminals T & T. If the relay pulls in but the burner does not try to fire, you need to check voltage (120) going to the motor via the orange wire. You will only have about 45 seconds to get this done before the safety locks out the burner.

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