Gas Furnace

[thebrisk]

I have a house built around 1956 with the original gas forced air heater. It has been upgraded with electronic ignition some time ago. It's been working great until 3 months ago.

The problem I'm having is that the unit won't stay on for more than a minute before the fan stops. I will hear the come on, then after about 50 seconds, it will turn off. After being off for a few minutes, it will turn on again. It cycles on and off like this, until the set temperature is reached, which of course, takes a long time.

I replaced the batteries to the thermostat, then I replaced the thermostat. This didn't help.

Any advice?

Thank you

[Hube]

What adjustable controls are on the inside of the unit. What is the high limit setting? What is the fan on/off setting? What model thermostat ? post back with info and we will advise. Hube

[thebrisk]

quote:Originally posted by Hube

What adjustable controls are on the inside of the unit. What is the high limit setting? What is the fan on/off setting? What model thermostat ? post back with info and we will advise. Hube

I collected the info. Here it is:

Thermostat - Honeywell CT3500A (Brand new - but I was having the same problem with a new Lux programmable thermostat I bought last year)

Heater Unit - Fraser Johnston Model 100 HN (Old - I'm pretty sure this is the original heater).

Fan setting - 110 & 135
Limit - 175

I have never changed these settings. The heater wasn't cycling on and off last year like it is now.

Thanks

[Hube]

Possible fan control is at fault. The existing settings are in range.( ok) Normally 125 on... 95 off, and high limit 180. but if was alright last year with the settings that you now have now, just leave them the way they are, and check for the faulty senser in the control. Hube