First off, there are furnaces and there are boilers. Kinda nice to refer to what you have with the right name.

A boiler heats with hot water, a furnace heats the air. Since your description involves water I would suggest knowing where the temperature/pressure guage is and what it tells you. And, how to add water if the level is low (i.e. the pressure) and when and how to add it.

And, keep your service contract.

I can't blame a layman or old timer for confusing the terms when in fact years ago there were hot water furnaces. And in fact still are outdoor open system wood boilers/furnaces.

You see the term furnace also depicted an open hot water heating vessel.

The proper term boiler became prevalent when describing a closed system vessel.

So going back to the 50's and before, when risers and open tanks were used in attics, sometimes with feeders, in fact they were "hot water furnaces"

judiec,

Any fix yet?

Being related to an appliance with a solenoid that uses water, I'm betting on a singing PRV on the boiler or it's the tank water heater, or piping.

Wiley0, thanks for clarifying furnace vs boiler. I have the unit tuned up every fall, and the temp/pressure gauge stays in the proper range.

z1700, I'm waiting for the repairman as we speak, and will mention the PRV when he comes. My plumber suggested the circulator on the water heater. I greatly appreciate the help - thanks!

Domestic hot water recirc? Very likey the culpret.

Small wet rotor, or big with motor, bearing assembly and pump end?

My guess if small wet rotor, installed wrong with can (motor) up or if other style, bearing assembly failing.

z1700, as you said, the problem is the '066 circulator', but I forgot to ask if it was installed wrong. It isn't covered under our oil company service contract, so our plumber will check it out later today, and get it on his schedule.

Thanks so much for all the help!

If it is a one piece sealed unit, the motor must never point up, which the end usually has the label. This causes air entrapnment and ruins internal bearings, and squeals. The quick draw from the washer would multiply the entrapment problem and you hear the motor moaning.

z1700, the plumber says the old pump was installed correctly, but was not circulating. It is a Taco 006 BT4, and it is bronze (or brass?). And replacing it wasn't cheap! Decided to add our water heater to our service contract, in case something else happens, since the heating/hot water system is 12 years old now.

Bronze pumps on domestic fresh water systems are required unless you wish to buy a pump every 1-2 years but better yet wish to wash in rusty water.

good luck