Circulator, not burner, short cycling?

GatesMan

Two year old 175K Crown 80% boiler with B&G circulator. I didn't notice it doing this last year - after the burner shuts down, the circulator cycles on and off over and over again until it's time for the burner to fire up again. The circulator does this for approximately 20 seconds each way, 20 seconds on, 20 seconds off. According to the thermostat, the system is keeping the house at the desired temperature very reliably. I turned power off and back on but that didn't make any difference.
Any help greatly appreciated.

delta T

What kind of B&G circulator, can you take a picture? was the pump replaced with the boiler?

STEVEusaPA

What kind of aquastat control are you using, and what are the settings.
Also I would check the amp draw on the circulator.

billtwocase

Sounds like motor is going off on thermal overload? Does it feel hot?

GatesMan

Thanks all. The pump is a B&G Series 100 HV. It was replaced with the boiler. It is not hot to touch.

GatesMan

The manual says this boiler uses a proprietary version of the Honeywell S9361A "integrated boiler control".

GatesMan

For what it's worth, I just ran through the settings on the control and they are all at factory settings, including "circulator over run" which is set at zero.

EBEBRATT-Ed

Something in the control system is probably set wrong. Does your thermostat have a heat anticipator adjustment? You may try adjusting that

Zman

You should be able to narrow down the problem by checking the power to the circulator as it is cycling. This will tell you whether it is a controller issue or the thermal protection on the circ.

Abracadabra

Take a picture of what is controlling the pump. Some boilers have a thermal balancing thermostat

GatesMan

Boiler control photo

GatesMan

Ok, I checked the circ amp draw and it never varies. It's either zero when it's not running, or 1.9-2.0 when it is, regardless of the burner status. The spec label on the circ says 1.9 amps.

Zman

Is the controller cycling the boiler? This would be a controller issue.
Or is the boiler providing constant power and the circ is turning off on it's own?
You either have a bad circ or a control issue, you need to figure out which.

Abracadabra

I assume no error codes shown on the control?
Can you video the control while the circulator is cycling showing the LED display? Move the wires out of the way.

GatesMan

Correct, no errors shown. When the burner is on, the circ is always on, and the led display reads 8/Running. When the burner turns off and the circ turns off, the led display reads 1/Standby. Then, when the circ cycles on and off without the burner, the led continues to read 1/Standby.
17/ Self Test is displayed momentarily when the boiler shuts down, followed by 1/Standby.

billtwocase

Does this system have a purge/dump feature? Sounds like it is at the end of a heat cycle, and is dumping the hot water?

GatesMan

I never even heard of purge/dump. It's a pretty simple system, as far as I can tell. And, as mentioned above, it keeps the house at exactly the set temp according to the thermostat.

Zman

Normally a pump post purge run a certain amount of time after a heat call. Perhaps crown has a new twist on that.
A call to tech support would put this to rest.

GatesMan

Yes, it does describe "purge" in the manual. I think it was the word "dump" that threw me. The system is supposed to try satisfying the thermostat with residual heat before firing up the burner. Unfortunately, the manufacturer doesn't seem interested in helping homeowners, only heating contractors, etc. I'll give the installer a call.

billtwocase

Sorry Gates, warm air systems, you have a dump when zoned. Same results. Sounds like the control has a post purge to me, and is not temperature controlled, but timed.

GatesMan

Boiler manufacturer (Crown) told me that what I was describing is normal purging operation, which I now kind of understand. It is both timed and temp controlled. Manual says purge start temp can be 140-180 (high limit is 180). I'm now trying to understand how adjusting the purge start temp effects general boiler operation, i.e., would raising the purge start temp cause the boiler to run less efficiently but bring the house up to the set temp quicker in the morning? It's a big, old, drafty, leaky house and it takes forever to bring temp up from overnight 62 to daytime 67.

Zman

The purge cycle should have no effect on setback recovery. It is designed to protect the boiler by circulating water until the heat from the cycle has dissipated.
If you are finding that the boiler and circ are cycling as you come back from a setback, it makes me think that the t-stat is causing the issue. The circ should be running during the entire call for heat.
With most houses, there is little or no energy savings in nighttime setbacks. Do it if you are more comfortable, not to save money. If you want to test this, do it one way for a month then the other. Check your bill ( adjusted for variations in degree days) and see for yourself. By the time you heat and cool the entire mass of the building, you are not really saving.

GatesMan

Thanks. I thought the purge function was about efficiency, trying to satisfy the call for heat with residual heat before firing up the burner.