Aquastat Question

Ron Schroeder

What model aquastat is it?

The Low limit sounds too low. If the fuel is oil, then I would suggest not setting the low limit below 130. This is not the cause of your problem but it will help protect the boiler from condensation.

If the problem is a mechanical high temp limit tripping, then set the Hi limit on the aquastat to 180 and see if the problem goes away.

The problem may also be worn out or dirty contacts in the aquastat. If that is true, then you would probably be best to replace the aquastat. I prefer the L7224U by Honeywell.

Bob C

I just got this from a friend. Any ideas on what to check. It sounds like the low limit is not working..

"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. "

Alan(CaliforniaRadiant)Forbes

Sounds like

the manual high limit is tripping. Either the boiler is overheating or the limit is set too low. Ask him what the highlimit is set at.

I sometimes see this happen when only a small zone calls for heat; the boiler fires and because there's not enough flow through the boiler to pull the heat out of the heat exchanger, the temperature increases very quickly and the high limit trips. A good reason to pipe primary-secondary.

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Bob C

the low temp is set at 120 and the high temp is set at 190

Alan(CaliforniaRadiant)Forbes

That's quite

a spread; it should be fine.

Does anyone else have any ideas?

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