burner turns off after a few seconds

[airhar]

I hope I'm on the appropriate forum...I'm a HVAC contractor specializing in primarily residential installs...my "tech / service" skills may be a little rusty. That being said, I am working on a Carrier 58STX furnace...burner lights then goes out after a few seconds...I measured the milliamps at the flame sensor and it was within the range stated on the troubleshooting /fault codes sticker (I seem to recall I read 5.4 mA). I was convinced it was the gas valve and replaced it but still the burner turns off. No limits are tripping and I jumpered the pressure switch to take that out of the equation...I'm thinking now that the circuit board must be the culprit...any advice?

[openclasspro]

Did you clean flame sensor with steel wool?

[dandyme]

what's the pressure switch seeing?

are you losing 24v to board?

just where are you losing the signal for heat?

so many ???, so little info..............

[JonesHVAC-R]

Did you clean flame sensor with steel wool?

Personally I would start here...

I have been to so many places where they have told me they had a clean & check recently and the flame sensor is dirty. A dirty flame sensor 9 times out of 10 is the culprit for flames coming on then going out.

[hvac wiz 79]

5.4 microamps ? did u just use wrong term ... if so idk what cleaning with steel wool would do

[chibulls21]

If you reading 5.4 micro amps thens its obviously not the sensor. You need to make sure you have 24 volts at the valve and the work backwards to see where your losing voltage. Is this lp or nat?

[jmac00]

I hope I'm on the appropriate forum...I'm a HVAC contractor specializing in primarily residential installs...my "tech / service" skills may be a little rusty. That being said, I am working on a Carrier 58STX furnace...burner lights then goes out after a few seconds...I measured the milliamps at the flame sensor and it was within the range stated on the troubleshooting /fault codes sticker (I seem to recall I read 5.4 mA). I was convinced it was the gas valve and replaced it but still the burner turns off. No limits are tripping and I jumpered the pressure switch to take that out of the equation...I'm thinking now that the circuit board must be the culprit...any advice?

Im just going to throw some ideas at ya:

does the vent motor continue? does the blower motor come on and continue?

If not, jump R to W that will eliminate the stat.

does the burners still drop out? ( I suspect you mean POINT 54µA Carrier maybe different)

Is there 24v to the gas valve? do you get a constant 24v or does it drop out?

(Just to be clear, is this a Natural Gas or Propane unit.)

Do you have continuity throughout the safety circuit, Roll out switches, limits

Put your Manometer on the Pressure switch, does it maintain pressure?

Have you checked the flue to make sure it's clear at the top.....Possible birds nest near the cap? (pressure switch/manometer will help with this)

If it's none of these, Put in Rheem

I kill me

[mlstark]

What is this DIY day?

[jmac00]

What is this DIY day?

we should have the Mods move the thread......oops, my bad Post reported to the mods

[Danimal535]

NO DIY some one can get blown up

[jmac00]

NO DIY some one can get blown up

it got moved thanx guys

[gravity]

if you have 5.4 adc then flame sensor is good. check to make sure the board is sending ~ 90 volts to the flame sensor.

check your pressure switch when the unit fires up. make sure this isnt dropping out your flames. check pressure switch tubing also.

let us know what you find out. dont leave us hanging

[bja105]

What error code is it giving you? No need to guess, its giving you the answer (probably.)