Surging pressure guage on hot water boiler

Randy Tibbits

I just got back from a sevice call on a older Weil mclain gv-6 boiler. Pretty typical call found a defective zone valve. But I noticed when I started the boiler back up the pressure guage needle pulsated for a bit and then settled down. The needle settled in at 20 lbs. Any ideas what could be causing this?

Steamhead

If it just did that for a couple seconds

the pulsation likely resulted from the circulator starting up and possibly the mixing valve reacting. If it took longer than that it might be steam boiling up thru sediment inside the boiler.

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