My central heating unit (Gas Heat) seems to have a problem staying on and running through a normal cycle. This has been an issue since I bought the house. (The A/C unit works fine) It appears to be intermittent on the 'heat' setting. It ALWAYS kicks on when it's turned on but most of the time it will shut itslef down after only a few seconds and then kicks itself back on again and goes through this cycle a number of times until I decide to shut it off. When it stays on it produces heat without a problem...the problem is it will not always stay on. I replaced the original thermostat in the house following the same wiring pattern as the original one as I thought that may fix the problem...still having the same problem since installing the new thermostat. Is it possible that the wiring on the original was wrong or something else altogether?
99% of the time with newer furnaces, 10 years and younger. It will be a dirty flame rod sensor. All you have to do is pull it out and clean it up with some sand paper, reinstall and run. The flame rod sensor has about 2 seconds to prove flame to the control board, if it does not see the flame because it is dirty, it tells the control board the flames did not light, and the control board cuts power to the gas valve. Then it starts the sequence over again.
The t-stat should be fine if call for heat. If the burners shuts down, possibly the flame sensor is wearing out. Or it has oxidation buildup due to climate conditions. Yes, you can temporarily clean it with fine sandpaper. But better to replace it. The flame sensor is also a safety switch which will shut down the gas valve when there is no flame present. This component prevents gas fumes leaks. But, first check the elect. outlet to the furnace (centralized) and check if you have the right polarization ( proper Hot and Neutral with ground). With new units the electrical circuitry requires correct polarization. And that's when the unit runs intermittently. If that doesn't work call a heating contractor.
If the burner is shutting off within a few seconds of coming on, the problem is most likely a safety control shutting down the system. There could be a number of reasons why this is happening. For example, a spill switch could be detecting the flame leaving the heat exchanger (or is faulty) or the cad cell (if you have an oil burner) could be failing to recognize that a flame is present and is stopping the burner to prevent filling the blast chamber with oil. If it heats properly when the burner actually stays on (cycles through the appropriate high/low limits and the fan comes on when the heat exchanger is warm), then I wouldn't think there's a problem with limit controls. Look to the burner and safety controls.
check that: limit switch will close and turn on fan when air temp in plenum is at a certain tremp. when the heating cycle is over and air tem cools down in plenum, limit switch opens and shuts off fan. i bet you have a faulty limit switch! don't confuse the fan relay with limit switch. fan relay is energyzed on call for cool from stat, (ac), or fan/on.
it feels like the two the sequncer is caught or the warmth relay is undesirable. they at the instant are not to no longer ordinary to restoration. in case you prefer to keep money, i'd flow to an condominium complicated and pay their upkeep guy to restoration it for you. he would be alot extra fee-effective than a warmth and ac guy.
