Short cycle in one zone

dbolo80

I have a 3 zone oil furnace system. The main zone and upstairs works fine, however when I turn on heat in downstairs bedrooms zone the furnace will constantly start and stop. Furnace will run for about a minute, shutdown, then startup up again right away. I have replaced the thermostat but problem still exists. Seeing the other zones work fine, I don't suspect upper/lower limits settings. I suspect it may be the controller for that zone. Any assistance or thoughts appreciated as the kids are complaining of being to cold because I won't turn on heat in that zone until I fix to save oil and possibly boiler damage. Thanks in advance

Zman

If you suspect the thermostat with a 2 wire heat only t-stat you can just connect (jumper) the wires to test proper function.
You may be air locked in that zone as well.

billtwocase

Pics always help. What zone valves do you have? What thermostat did you replace yours with?

dbolo80

I am 95% confident its not the thermostat. I changed it with a basic manual t-stat (two wire) as seen in the photo the taco valve on left runs the troubled zone. If its air lock, can I remove it from the valve above it as I dont see an air relief on the zone....

really appreciate the assistance

icesailor

dbolo80 said:

I am 95% confident its not the thermostat. I changed it with a basic manual t-stat (two wire) as seen in the photo the taco valve on left runs the troubled zone. If its air lock, can I remove it from the valve above it as I dont see an air relief on the zone....

really appreciate the assistance

Is the basic 2- wire thermostat a Honeywell round T-87?

If so, did you set the heat anticipator to 1.2 amps? If you didn't, you might have destroyed the thermostat.

Or, you have a bad power head on the zone valve and the piston isn't traveling to the bottom of the throw and it is tripping the connection between #2 & #3, just barely. When it is doing it, put your finger on the manual lever and see if it will push further down. If it does, and the cycling stops, change the power head.

Either way, check the heat anticipator setting.

If the burner comes on for 10 seconds or less and stops, then a few minutes later, it comes on for 45 seconds and stops, then a few more minutes of being off, the burner starts again and runs for two minutes, then cycles again and continues to run and continues a cycle, change the thermostat. You've lunched the anticipator. If you bought an El Cheapo thermostat like a square Honeywell T882, without the baseplate, and you can't set the anticipator any higher than .8, replace it. It won't work.

That is a promise.

dbolo80

I bought the cheapo honeywell as a test. I can reinstall the smart one, the cheapo unit allows for actuator change and I set it to .5 ill push it up and try the test on the head..... Ill post update after test thanks...

icesailor

dbolo80 said:

I bought the cheapo honeywell as a test. I can reinstall the smart one, the cheapo unit allows for actuator change and I set it to .5 ill push it up and try the test on the head..... Ill post update after test thanks...

Setting it on .5 will make it do what you describe. If not outright blow the anticipator. If you put an electronic/digital thermostat on, some require a isolation relay. The Taco 57* zone valves require .9 amps to operate. If you can't set the anticipator to at least .9 amps, they won't work properly.

Taco instructs you to NOT jump out a thermostat to test the power heads. Those valves are bomb proof. Unless you futz with the fuse.

More likely, you had a bad power head. Now, its a stale sandwich with green on the bread.