are you gettingheat all over??, what is the water temp. you usually start out with a 12 lbs. on a cold start if things are adjusted right and as the water get hot the pressure will go up some maybe to 20 lbs or so depending on the pressure in your exspantion, and size of the tank. Is the burner coming on too often also.
A pump running full time could be relay stuck, zone value end switch stuck, one stat bad,
or a bad low volt wire shorted out. Is you pump on the return line?? Is your zone value open when the pump is running full time. If the zone value is open and pump is on the return line it should not hurt it to run full time as long as it is moving water. Hard to tell what is wrong without seeing and testing. Later paulbm

Thanks paul,

This evening, with the heat having been turned off for the day and the system cool, the circ. pump finally turned off completely - all is quiet.

Our heat seemed normal in recent days, but I didn't pay close enough attention to the basement zone. With the heat off now, temp is 150 at 12 lbs.

When I turned the thermostat up 1/2 hr ago, pump began running immediately (but much quieter than previously) and has been humming ever since - even after several minutes of turning both thermostats back down.

The pump is on the supply side prior to the zone valves and yes, one is open (the main house loop). I tested the 2nd zone, at it works fine, as determined by supply pipe suddenly getting hot afterward (but cool before).

I turned down both thermostats (10 minutes ago) and the circ. pump is still humming.

Not sure whether to cancel the service call or proceed. Circ. pumps are supposed to cycle on/off as necessary, correct?

Thanks again for the help.

If you have zone values and both close and no wild loop, then the pump should go off as soon as the zone valve closes, because there is no place for the water to circulate to, so your pump would be dead heading and that would make it heat up too hot. even when the water temp is 170 degrees on the return it is still cooling the pump. There is a little leaver on the end of the zone value
it is spring loaded . watch that leaver and have some one turn up the heat. You should see the leavers move to one side and then make sure the move back when you turn the heat down. If a zone sticks open it would run the pump, but it should run the burner also. I don't know is you have a separate
relay for the pump and burner or not. If the pump does have it own relay it could be sticking some times. I hope your dealer did not put your pump on a
temp. sensor to turn off. later paulbm

Thanks again for your help, paulbm.

Just to update, tech is here this morning (9:25 am thursday E.S.T.). Even though I shut off the heat an hour ago, the pump was still running when he got here. Appears to be some sort of controller problem.

He went to the supply house to get a relay which will control the pump. He said there isn't one currently, but instead some other sort of controller that this Hydrotherm unit has (which he's not sure how it works, but it's not typical). Anyway, that controller is going to get disconnected and replaced with the relay that will shut off the pump when the zone valves are closed, etc.

Thanks again for the help!

Another update: It's not over yet. Two relays were installed - one for the pump and the other for "the other thing (I forgot).

Upon testing, another issue was uncovered, which perhaps we always had. The main (upper) zone is not flowing sufficiently to return water back to the furnace (but basement baseboard zone works great). Effectively, the first radiator in line upstairs gets really hot, but each subsequent one less so, so that the last one (there are 8 total, some are quite small) takes forever to heat and is only lukewarm at most. We tried to bleed, and also attempted to free up what was thought to be air lock - to little avail. I then had an addl. boiler drain installed (past the upper floor zone valve) to try to aid filling the loop backward to unlock the system. For some reason the water would not seem to flow in reverse. Lots of fussing around trying different things, and eventually it was filled the hard way.

Still, pump circulation is impeded for that zone. Tech suspects the pump may not be sufficient for pushing past the diverting tee set-up that we have supplying the radiators. He's going to check with TYCO etc to see what's recommended for a set-up with diverting tee's (it's a 3/4 loop that reduces to 1/2 with a 1/2 bypass at each radiator.

Sorry to belabor this, but any knowledge appreciated in the meantime. Thanks.

correction: I meant to say the upper zone doesn't seem to return HOT water, which says something about pump operation in that zone. (The lower baseboard loop works fast and great.)

It doesn't sound like you are done yet. they probably had your pump operating
on a aquastat that keep it running until the water temp cooled down, which is a no no on a zone system. Did your service man check to get air out on the second story and make sure the feed value is putting water into the system so you can get enough pressure to get air out and make the upper story work. I just went back and checked your first post and remembered another factor. you have a two story and basement. boiler in basement? if so you need to check to see if you 007 taco pump is the smallest one they make, i think it is.
The small taco pump does not have very hi head pressure, i think only about 7'. i lot of guys that do boiler work don't know this ,thats why they use them.
I always go to the next size up on a house like yours. I don,t have the no. in my head. later paulbm

Your aquastat comment (temperature-controlled) describes exactly what seemed to be happening. I'm glad that was corrected today...wish we knew it two years ago when it was zoned! Ugh.

As for the serviceman getting air out on the 2nd floor, at some point he did, but first he tried to fill the system in reverse right away (he closed the gate valve between the supply and the zone valves, opened the newly installed boiler drain beyond the zone valves.....that's when nothing was heard flowing through the feed, and only some infrequent trickles when the supply and zone valve was opened manually a bit (at this point the feed was silent unless the zone valve was opened). Then he filled the system a bit the regular way, removing some bleeder pins upstairs as part of that process. (He never did get the water to flow backward through the loop and out the boiler drain.)

Is the next size TACO pump likely to produce more equally heated radiators (as opposed to first in line getting most heat, etc down the line). Seems so, and that would be a wonderful thing.

Question: Do you first need water in the system to get enough pressure to get the air out? I think that's what you're saying, but not sure. (I'm curious about the physics behind that.)

As for the current TACO pump, the service man did also mention the possibility of insufficient head pressure with that pump. But he wanted to check on that further and get back on that. Thank you for confirming that!

Yes if you have a higher pressure it is easer to push the air out. its the same way to circulate, if you pressure is to low it will not want to flow to the upper story, especial if the pump is too small. If you go to the hi velocity pump,and thats what i always use in a three story house, you will have one little thing you may not like. On a zone system , when only one zone is open you might hear a little water movement noise depending on you piping system.
Engineering will vary from one engineer to another a little. But i am going to give you some facts. normal hot water system no more than 30' to 40' of radiation on one 3/4 in. loop or zone and standard zone values 3 to 3 1/2 gal.s per min. . Now if you have too long of loop you will slow flow down and lose too much heat, same if you have too much radiation on a loop. You said
three story two zones. this sounds like long loops which means hi head pressure, and maybe too much radiation per zone. some times when i run into this i advice the owner that we will have to switch the zone values to a full flow zone value, they go up to about 7 gal.s per min. flow, this along with the hi head pump will take care of too much heat loss,and too much head pressure.
I hope all this is not confusing you too much, But hot water in a older home can be a little complicated. and a lot of guys do not understand this.
You can check a zone out one way by checking the temp leaving the boiler and then check the temp. coming back from the zone. no more than 15 degrees drop.. Later Paulbm

Thanks very much. First of all, it's a relief to now go check the boiler with heat off and have the circ. pump quiet (off).

The house dimension has a 33'x25' footprint, and it's a single loop that runs the perimeter of that rectangle. There's just a single riser (1/2" tubing) that tees off the loop to supply two adjacent small radiators in series) up there. They are 24" narrow profile radiators - not much, but it is what it is up there. If that sounds like a prescription for bumping up the pump size, I'm up for it.

As for the temp drop, currently it's way over 15 degrees for at least a half hour (hot supply, but cool return even after 1/2 or so - give it an hour more and the return is just "warm" to the touch. So it seems the larger pump is a "go".

This experience yet again confirms my notion that good plumbing & heating professionals are like doctors (and should not be utilized "on the cheap".)

Sounds like your getting it. is this a 3/4 " loop? If the zone valve is 3/4 " you might want to go to a full flow zone value. Because a standard zone value only
flows about 3 to 3-1/2 gal.s per min and a full flow is 7 gal.s + They look the same but the hole inside is larger. a lot of the younger heating guys are great on new homes. But a lot of them don't know the old houses. Don't know how it is in all the states, but in Mi they have the law so a mechanical license can install a boiler in a home , even though he has never been a boiler man. I really don't think this is right but thats the way it is. When people ask me at least i can say i do have a 3B license which go way beyond house hold boilers. Later paulbm

Yes, 3/4" loop (except for the short 1/2" legs between each pair of reducing tee's under each radiator).

Since the basement baseboard zone is fine, does that mean I might just upgrade the other zone valve (radiator loop) or do both? And would I do that along with getting the next size pump, or just try a full-flow zone valve alone first?

I got a message this evening from the serviceman. He has a solution (not sure what, yet), which involves making some changes and also installing a balancing valve. No details to share yet, but I'm happy to do so when I hear from him. I'll definitely mention your suggestions. Thanks again.

i would go with both HV pump and full flow zone value. your service man might want to put balance value on basement loop to try to get upper story to work, but i do not think that will work. You need more head pressure and more volume of
water to make it work. if you are saying that your 3/4 in. main comes to a radiator and then it has a 3/4x1/2x1/2 tee, and at the other end of the radiator
it goes back into a 3/4 pipe, this would be called a mono-flow system. A mono system always need more flow and head pressure than a loop system. You haven't said if your basement is a 3/4 loop or is it like the mono system in the main floor How many radiators are down there. you could always try leaving that zone value in there. Because it down low it does not take as much head pressure to work. keep in mind you would get 5 lbs of pressure at the boiler just from the weight of the water. so if you exspantion is large enough it would not hurt to start out on cold start with about 16 to 18 lbs.
Just watch it when the hole system get hot that it does not go beyond 26 lbs.
Later Paulbm

Really need some help on a Weil- McLain in floor heat boiler ?