Is boiler cycling too fast?

captainal

We have hotwater baseboard heat that isn't putting out enough heat in cold (zero degree) weather. The boiler was new 5 years ago and is a Lennox GWB8-1E. The temp on the "hydrostat" is set at 200 degrees and the boiler goes on and off every 5 minutes. The thermostat on the wall is set for 70 and the temp never gets above 60. It is a closed loop system with 3 loops, all of them 1/2". Is it possible that the circulation pump doesn't have enough flow?

BobC

Are you sure the pump is moving water? Post some pictures of the boiler, the pump, and the piping coming from the loops.

Bob

captainal

The pump is moving water. All 3 loops have some degree of heat coming off the baseboards. The shortest run (22 feet of fins) has heat at both ends. The longer runs (31 & 32 foot) have some heat at the first baseboard (both approx. 4 foot), but it drops off rapidly by the next baseboard.

Jamie Hall

You don't have enough flow.

First question: did it ever work? I'm presuming it did...

then the question is, why has the flow dropped? Is the pump running at all? "Some degree of heat" may be just natural convection. Is it running, but running poorly? Is the impellor damaged? Is there air in the system making the pump cavitate? Is there a partly closed valve somewhere?

captainal

There is only 1 pump, it is mounted on the boiler. 1" dia copper from the pump.
One loop (1/2 inch, 31 feet of fins) is tee'd off and the main line is than down to 3/4 inch. A zone valve (controlled by a second thermostat) is next in line.
The second and third run are tee'd off of the 3/4 inch (after the zone valve) and are both 1/2 inch. One loop is 22' of fins and the other 32' of fins.

captainal

Thanks to both of you for your input. I have checked both the pump motor and the return water line with a "screwdriver stethoscope" and can hear the motor running and water flowing.

The boiler is 5 years old and the heat was always a bit on the low side, but much worse this year.

captainal

How often should the boiler be cycling???
5-7 minutes on, followed by 5-7 minutes off seems to fast.

Hatterasguy, Is the name for your location or your boat?

Fred

What kind of thermostat are you using? Is it properly set for hot water heat, 2 or 3 cycles per hour? Most thermostats have a factory default for forced air at 5 cycles per hour.

captainal

Both thermostats (one for on-off and one for the zone valve) are the cheap Honeywell round CT87K. Cycle rate switches were set per the instructions for hot water.

The rapid cycling I get is caused by the "hydrostat" on the boiler, not the thermostat.

BobC

To be certain short out the thermostat terminals and see if the cycling stays the same. If it does it means the boiler can't get rid of the heat. Are you sure the water is getting up to the setpoint?

Bob

bmwpowere36m3

I'm curious how the "loops" are tee'd off... if in fact it's just a regular tee, then there is no reason for the water to flow to those branches. Water will take the path of least resistance and that may be just down the main 3/4" line and back. That's if I understand the layout correctly.

Pictures or a schematic of the system piping would help tremendously.

captainal

I have watched the thermometer/pressure gauge on the boiler. The boiler will fire and the temp goes up to the 200 degree set point which turns the boiler off. Temp will then drop to 180 and the cycle will repeat. 5-7 minutes on, followed by 5-7 minutes off.

captainal

bmwpower (old Z3 for me)
The first loop is tee'd off with a combination reducer tee. I" input, 1/2" tee'd off, 3/4" thru. The second tee is 3/4" input, two 1/2" out. All 3 loops are 1/2". Return lines are tee'd in a similar manner.

Hatterasguy
The pump is a TACO 007. I will try to get a couple pictures posted yet tonight. (need to charge camera batteries) The boiler is rated at 75,000 btu input, 62,250 btu output.

hot_rod

Any Y strainers in the piping. It sounds like a flow blockage somewhere.

captainal

Our house is a 1960's era 4 level split. The boiler is in the lower basement. It is approx. 5 vertical feet from the pump to the tee's and the one zone valve. The uppermost loop is in the bedroom area which is an additional 9 feet. The total vertical height would be approx. 14 feet from pump to highest baseboard. Would this affect the pump capacity?

captainal

Hot rod,
As far as I can tell there are no Y strainers in the system.

captainal

Pressure gauge shows 20 psi.

hot_rod

You could take some simple, quick temperature readings and get some flow ideas.

Get a digital barbecue thermometer with a flexible probe end. Wrap a rag around the probe where it touched the copper tube tightly to get a good reading.
Measure temperature going into the baseboard loops, and at the far end. This will tell you what temperature is actually being delivered and that it is flowing across the loop.

captainal

I'm attempting to get the dealer out here tomorrow to do the temp checks on the loops as suggested.

Hatterasguy, Should I have him lower the pressure??

captainal

Thanks to all of you for your help and advice. It's not going to be too cold tonight (+5) so I'll just throw another quilt on the bed.

My plan is to raise hell with the installer and cover the issues as outlined by hatterasguy.

If it is a pump issue, that should be covered under warranty. Any sort of blockage should have been caught and flushed out during installation. It isn't that old. I think I have a decent case.

I'll post the results tomorrow.

p.s. forecast in Minneapolis for tomorrow night is -12.

captainal

Hatterasguy, I very much appreciate your insights.
This morning with outside temps at +10, I was getting good heat out of the baseboards in 2 of the 3 loops. The loop that is under-performing is the uppermost in the house. Copper tubing temp just warm to the touch (100 deg?) at beginning and end of loop, no noticeable temp drop. This is for the bedroom level of the house and is about 9 feet above where the loops are tee'd off. Is some sort of air block possible that is preventing circulation of this loop?

Rich_49

Please tell us what type of baseboard you have and the tubing size within the enclosure . Would the upstairs zone happen to be the one with the most emitter installed and which tee is it installed on in the basement ? First 1" x 3/4" x 1/2" tee or the 3/4" x 1/2" x 1/2" tee ? If it is on the smaller tee could you tell us whether it is on the branch connection or the through connection ?

aircooled81

High flow - low temp difference, low flow - high temp difference.
Warranty after 5 year instal, doesn't sound like peery mason needs to get involved.
air at the coils/convectors upstairs, very possible. air slowing down flow, very likely.
boiler short cycling because flow from secondary loops to primary boiler loop insufficient, very likely.
pumps can spin the motor and not the impellar. I have seen the taco plastic impellars break-off inside. doesnt stop the motor from spinning.
I have also seen pumps build-up modules inside over the years, where the valute starts to get smaller at the inlet and outlet. this can impeded flow. 4 allen screws hold the pump motor to the valute, then the pump can be opened up to see if there is a blockage or impellar issue.

I really like the posts from hatterasguy,
i think those pics everyone is asking for helps put them in the boiler room with you. things you think are normal, stand out to wallies!