thermostat flashing "heat on" -burner often doesn't light

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Old 03-17-09, 09:30 AM
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thermostat flashing "heat on" -burner often doesn't light

my thermostat will often flash "heat on". It will flash 4 times, then a slight pause, then will repeat again. when furnace is on, it will stay on continuously (it doesn't flash) I think I read in the manual at one point when it was here that it meant that the furnace had exceeded it's number of heat cycles/hour? the furnace installed took the manual, said it is not for the home owner. they said they did not put limit on cycles when they programmed it. I had heard somewhere that it could be shutting off because of heat overload, but I don't think that is the case. I can get it to run when it is flashing by turning up temp? The temp was set at 70 and temp in room was 70 with thermostat flashing. I turned heat up to 72 and the "heat on" stopped flashing and came on continuously and the furnace started. the furnace often short cycles-comes on and will only run for a few minutes then will shut off. THis is not associated with the flashing thermostat, at least I don't think they are related.

I have new furnace and thermostat and have had nothing but problems with the system. often the burner will not light. It arcs but doesn't light. they replaced the nozzle and replace fuel lines, filter. It was leaking but thay has stopped since they replaced everything. previously they replaced nozzle with the wrong size but put correct one back in. supposed to be .75 70B and they had put in .65 70B. just adjusted the air mixture said it was letting in too much air. flame will sometimes just go out and it will try to light itself and sometimes is able to but other times it does not and the blower continues to run but blowing cold air. sometimes the reset light will come on , other times it does not. FYI this is a power vented system. brand new fields unit . it seems to work fine. comes on seems to pull constand draft (by looking at barometric draft regulator) to my knowledge, they have never measured the draft, despite my asking them about it on numerous occasions. they said it is working fine and just adjusted it "by eye".

furnace carrier 58VMR120-11120 riello burner, variable speed blower

thermostat carrier TP-PRH01-A programmable with humidistat
 
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Old 03-17-09, 05:29 PM
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You can always get it to go by simply manually bumping up the stat a couple degrees? Yet it will not come back on if you let the stat cycle naturally?

Is your system heat only?, with a heat only stat? Or do you also have a/c? Or do you have heat only, but have a heat and a/c stat?

Has this problem always occured from time to time? Or, is this some new out-of-the-blue problem?

And you can fix it by simply turning up the stat without first shutting it off or lowering the stat first before raising it? Seems odd the furnace will come on just from raising it higher.
 
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Old 03-19-09, 12:29 AM
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no, it will come on if I don't do anything and just let it sit with the heat on flashing. but it will come on immediately if I turn up heat. so it wouldn't seem to be an over temp limit.

system is heat and AC. AC has not yet been running as system put in in NOvember. problem with burner going out has been intermittant. first time they said due to water in tank. the heat on flashing has always occurred.

stat is heat and AC. a top of line programmable humidistat that has capability to turn on blower and humidfier but not burner if humidity is low even without a call for heat. I think it does same for dehumidifying. I can adjust humidity on the stat. getting this to work correctly was a real chore for them and not totally sure it is correct since my house is so open due to the construction that the humidity never seemed to come up even though it was running and moving water through the supply. I could tell because we used hot water and the pipe will get hot.
 
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Old 03-19-09, 08:17 AM
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Reason I asked about if a/c is associated with the unit or stat is that MAYBE you do not have enough degrees separation between the a/c and heat settings, and this is causing the problem. However, this problem should only occur with the a/c-heat AUTO setting - and not if you have the stat set to heat only.

You mentioned about water in the tank. Water in WHAT tank?
 
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Old 03-19-09, 09:34 AM
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in heating oil tank. that was corrected. I completely drained tank and while it was empy I cleaned it! yes I hosed it down with pressure washer to get all gunk out of it and then let it dry before getting new shipment of oil. And when the burner going out issue started happening again, I went to tank and disconnected the fitting at the valve and then opened valve to drain a little oil out of tank and it looked clean with no separation of water layer.
 
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