Gas and Oil Home Heating Furnaces - Gas furnace cannot start

Hi,

I have a natural gas heater, which is 8 years old.
Now it's takes about 1 hour to start heating:

1. Exhaust fan/blower motor (the one connected to the 2" PVC pipe) stars working.
2. No actions from the ignitor for a long time (in a normal conditions I can hear a click, then pilot light comming and main burner starts).
3. Sometimes after 1 hours heater starts, but stops after ~20 min (burner stops, system trying to restart by igniting a pilot and after 5-10 attempts only exhaust fan/blower keeps working)

Note: Couple monthes ago a had a problem when pilot had to restart 5 - 20 time before the main burner starts.

Please help.

Thanks in advance.

make sure that your intake pipe and exhaust pipe are clear, then be sure that your drain lines and trap inside furnace are clear. sounds as if the pressure switch isnt closing every time like you have a blockage somewhere

I've checked all rubber pipes
1. from exhaust fan to pressure switch
2. from pressure switch to furnace area, where the ignitor sits
3. the one connected to the elecronic valve from the furnace area, throught the 3 way splitter

All looks good for me.

When heater restarts ignitor does not event try to start for a long time.
In what conditions ignitor use to start? May be I have a problem with pressure switch?

Thanks for the help

I would estimate that over 75% of the pressure switches replaced are done so needlessly. The problem is almost always a venting problem. Horizontal runs of the vent pipe improperly sloped or supported are major problems.

I assume that in order to turm pressure switch exhaust fan should generate enough pressure.
I've disconnected pipe, which is running out of exhaust fan to pressure switch, but I did not feel a lot of air flow.

Could someone explain the process when pressure switch flips? and what to check in order to make sure it's working properly?

I see in my heater 2 major problems:
1. Pressure switch flips ~20 min after exhaust fan start working. Do I have to replace fan? or something check inside it?
2. When ignitor starts a pilot light and then gas blows - gas stops burning and it takes 20 -30 attempts to get gas burning. Where is a problem here? pilot light is not strong enough?

Thanks in anvance for a help

It is possible that the fan is going bad but also possible the heat exchanger is fouled & not allowing air to flow thru it as it should. Without removing the fan & testing, it is going to be hard to determine which.