Radiation adequate before, but now it isn't?

Chapman Flack

Friends had me over for the Super Bowl. Their house was chilly. They said
their system always used to be adequate to heat the house except for this
winter, but this year it's not keeping the temp up on the colder days. Said
their heating tech had been out multiple times and didn't know what to do.
Replaced the Aquastat (L8148J) on one visit, replaced the circ on another
visit. $$ but no improvement.

I asked if I could poke around a bit. They have an elderly hot water boiler
rated 125,000 btu/h input, 100,000 output on the gas side, 75,000 btu/h on the
water side. The house is in three zones with 24VAC thermostats and zone
valves, and a single circ located at the boiler on the return.

While I was there, they had all 3 thermostats at maximum setting, so all 3
zones had constant heat demand. All 3 zone valves were open, as they should
be. The circ was running constantly. The burner was cycling (on high limit
I'm sure), about 3 minutes on, 7 mins off, 3 on, 7 off....

So the burner was running about 30% of the time, or giving an average 30,000
btu/h gas output. I'm thinking that means the water flow is reduced or
radiation impaired for some reason so only 30,000 btu/h are being carried
away from the boiler. And this must have happened over time. They didn't
notice a problem last year. But looking at their house maybe 30,000 btu/h
is about right for the house heat loss, so maybe there's been a gradual loss
of flow/radiation capacity over the years, but last year it was still a mite
over 30,000 so they didn't see a problem, and now for the first time it's
dropped below the heat load for the house and they have problems on cold days.

Can something like that happen because of sediment or scale buildup in the
lines or the boiler? Does that sound likely? Is there treatment for that?
Does anything else sound more likely? I guess the new circ could be
undersized, but presumably the tech chose the right replacement for the old
one.

DIY Homeowner

Circulator

Is the circulator going bad?

Chapman Flack

It's a brand new circ

It's a brand new circ. Maybe the OLD one was going bad ... but then you'd expect the new one to improve the problem, and it didn't.

-Chap

kk_2

Baseboard?

Do they have baseboard? Could the fins in the baseboard be clogged up with dust/pet hair/whatever?

Chapman Flack

yes, it's baseboard

It is baseboard. I suppose it would be worth checking for free air flow. They tell me the baseboard units feel *cooler* this year than usual. I think I'd expect them to feel warmer, if the problem was restricted airflow. So I'm thinking low water flow is more likely. That or an insulating layer of crud inside the pipes, slowing the heat transfer to the fins.

Maybe what they should do is measure the supply and return temps. (Hmm, I didn't see any conveniently installed wells to allow that.) I guess if the designed drop is supposed to be 20F, if it's *more* than 20F that would suggest low water flow, and *less* than 20F would suggest bad heat transfer in the baseboards. Hmm. Something to try.

-Chap

DIY Homeowner

hmmmm

Maybe scaling. Hard water?

Fred Harwood

Delta

Actually measure the temperater of the boiler water leaving and returning. Use an infrared temp measurer, and only on black iron fittings (no copper or other shiny pipe). On such problems I usually find either low boiler temp or excessive delta, which often means pump problems or some restriction or boiler bypass problem.

You should see about 200-degree water leaving the boiler and 180 or so returning on a "design day."

Chapman Flack

Weird Honeywell zone valve/actuator mismatch ... ?

Was over looking at my friends' baseboard system again. The low-output problem turned out to be less involved than I'd thought, but we uncovered an unrelated problem: zone 3 won't shut off even when the thermostat is satisfied.

The system has one circ pump and three zone valves. The valves are Honeywell with 24vac motorized actuators; they say V8043E. The misbehaving one, zone 3, is obviously newer and shinier than the other two; it's been replaced some time. It says V8043E and also says 8840 on the other end. The valve was open, water was flowing, the pipe was plenty hot. I unhooked the wires at the valve to make sure it had no power, and it didn't close. Nothing even budged. (The two other zone valves made perfect working examples to compare to.)

When I took the actuator off the valve, the actuator by itself moves smoothly. The valve by itself is easy to turn. I can spin it from full on to full off between thumb and forefinger, and hear and feel the water start and stop.

No, the problem is only when you put the actuator ON the valve. It FITS, it just doesn't fit RIGHT. The valve shaft sticking up has two flats, and the socket in the actuator is the same way, so they only line up one way. But ... they DISAGREE by about 90 degrees.

The valve stem in the pipe has to be turned almost full ON before it will mate with the actuator in the OFF position. So when the actuator's off, the valve's still almost wide open. And when the actuator wants ON, it can't go far enough to make the end switch, 'cause the valve doesn't have that much farther to go.

I thought about trying to mount the whole actuator turned 90 degrees, but the shaft hole is off-center so there's only one mounting choice. I can think of two possibilities: either there's some way the valve itself could have been installed wrong and it'll mean draining the system and taking the valve out to reposition it ... or there are different models of actuator with subtle differences in shaft position, and this is the wrong one for this valve.

Has anybody seen an issue like this? If it's a matter of different actuators, how can we be sure to order the right one?

-Chap

Chapman Flack

Well ... that was easy ...

Dug out a thermometer and measured the supply and return headers as suggested here. Told an interesting story. Last weekend I didn't closely check the limit setting on the Aquastat, because (a) it's in an insane stand-on-your-head kind of place and (b) I knew it had been installed by a trained, qualified professional.

So the TQP left it set at the minimum position, 140 F. No wonder this 100,000 btu/h boiler could only run 3 minutes out of every 10! My friends told me the guy changed the aquastat on a call for a different problem, and the low-output has been since that change, so that mystery's solved. Set it up to 180-190 and the house is nice and toasty again.

Did run into a strange unrelated problem though ... I started a new topic, Weird Honeywell Zone Valve / Actuator Mismatch:
http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=13763&mc=1

Cheers,
-Chap

Chapman Flack

Well ... that was easy ...

Dug out a thermometer and measured the supply and return headers as suggested here. Told an interesting story. Last weekend I didn't closely check the limit setting on the Aquastat, because (a) it's in an insane stand-on-your-head kind of place and (b) I knew it had been installed by a trained, qualified professional.

Seems the TQP left it set at the minimum position, 140 F. No wonder this 100,000 btu/h boiler could only run 3 minutes out of every 10! My friends told me the guy changed the aquastat on a call for a different problem, and the low-output has been since that change, so that mystery's solved. Set it up to 180-190 and the house is nice and toasty again.

Did run into a strange unrelated problem though ... I started a new topic, Weird Honeywell Zone Valve / Actuator Mismatch:
http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=13763&mc=1

Cheers,
-Chap