HVAC

Ask a HVAC Question, Get an Answer ASAP!

Have your own HVAC question?

HVAC Technicians are Online Now

characters left:

Not a HVAC Question?

Question

Ocasionally my forced air will not cone on when I turn the thermostat. the glow plug comes on, some kind of blower sounds then it goes out. the burners do not ignite. other times the glow plug will come on 2-3 times and burner will then lite and fan will then start. When the burners do come on, I hear a "click" which I believe is in the gas valve. Correct? when the unit does not ignite and turn on, I will go out and turn off the "tripper" then on. I come in and turn on the thermostat, and the whole thing will then work. What has this (turning of tripper) to do with the operation of the unit.

Submitted: 286 days and 2 hours ago.

Category: HVAC

Value: $15

Status: CLOSED

Posted by Mark Henley 286 days and 2 hours ago.

Answer

Hi,

The furnace is locking out on a safety control during start-up , It is more than likely the pressure switch or the flame sensor. The flame sensor can be cleaned but you will need a manometer for checking the pressure switch.

Thank you

Mark.

286 days and 2 hours ago.

Reply

Have cleaned the flame sensor before, but will do it again. What does the pressure switch measure, gas pressure, or?

286 days and 2 hours ago.

Reply

Have cleaned the flame sensor before, but will do it again. What does the pressure switch measure, gas pressure, or? Still need to know if you know why It works when I trip the tripper.

Posted by Mark Henley 286 days and 2 hours ago.

Answer

Hi,

Gas or air, it is a water manometer. You will need one with a low range, they call them slant tube manometers about 50 dollars. I use a digital one but thats a bit pricey.

The manometer does the measuring , the pressure switch is monitoring a differential pressure that the vent blower creates through the heat exchanger. If it doesn't see enough differential then it doesn't allow the ignition to operate, you can check the flue to see if it is blocked that is one reason that a switch wouldn't make.

Thank you,

Mark.

285 days and 16 hours ago.

Reply

Still no idea on what snapping off the tripper has to do with the situation. In other words why the heater will turn on when you do this ???

Accepted Answer

Hi,

I'm sorry if I misunderstood, I am thinking you are referring to the breaker when you say tripper ? If that's the case and it is killing power to the furnace it causes the safety circuit to reset and then the sequence will start over again.

Thank you,

Mark

Accepts:
Expert:	Mark Henley
Pos. Feedback:	99.2 %
Answered:	2/10/2009

Journeyman Technician

UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

HVAC

Have your own HVAC question?

Related Hvac Topics:

Question

Answer

Hi, The furnace is locking out on a safety control during start-up , It is more than likely the pressure switch or the flame sensor. The flame sensor can be cleaned but you will need a manometer for checking the pressure switch. Thank you Mark.

Reply

Have cleaned the flame sensor before, but will do it again. What does the pressure switch measure, gas pressure, or?

Reply

Have cleaned the flame sensor before, but will do it again. What does the pressure switch measure, gas pressure, or? Still need to know if you know why It works when I trip the tripper.

Answer

Reply

Still no idea on what snapping off the tripper has to do with the situation. In other words why the heater will turn on when you do this ???

Accepted Answer

Hi, I'm sorry if I misunderstood, I am thinking you are referring to the breaker when you say tripper ? If that's the case and it is killing power to the furnace it causes the safety circuit to reset and then the sequence will start over again. Thank you, Mark

Related HVAC Questions

Hi,

The furnace is locking out on a safety control during start-up , It is more than likely the pressure switch or the flame sensor. The flame sensor can be cleaned but you will need a manometer for checking the pressure switch.

Thank you

Mark.

Hi,

I'm sorry if I misunderstood, I am thinking you are referring to the breaker when you say tripper ? If that's the case and it is killing power to the furnace it causes the safety circuit to reset and then the sequence will start over again.

Thank you,

Mark