On Dec 1, 9:46 am, Maury Markowitz wrote:
I'm having a problem with my Coleman Evcon furnace that I'm hoping
someone might recognize.

Basically the furnace turns on and operates fine, but then after a
short while will turn back off again. This happens quickly enough that
the house never gets a chance to warm up to the set temperature. The
thermostat is still calling for heat (there's a light) but the furnace
ignores this and remains off.

Resetting any part of the system makes the furnace come back on
immediately. What I mean is that if you pull the batteries on the
thermostat and put them back in, up it goes. It also happens when the
thermostat changes programs, from night to morning for instance, which
I _believe_ cycles power on the control circuit. This also works if
you cycle the power on the furnace itself.

I have a _feeling_ that the furnace control board is getting into some
"state" that makes it ignore the fact that the heat signal is turned
on. Resetting the electronics fixes the problem. But if this is the
case, wouldn't the status light be trying to tell us this? Throughout
everything the service light has remained a perfectly steady green.

I just pulled the filter and it definitely is a problem. But again, if
this was the problem wouldn't there be some indication? Why would the
furnace simply shut down?

Maur

You said: "after a short while will turn back off again"

Define a "short while". 30 seconds? 5 minutes? Time is relative.

Does the blower come on? If the filter is so dirty that it is
restricting air flow, you could have an over heating problem and the
furnace may be protecting itself by shutting down.

(I once worked for an IT Director of a major corporation who would
pretty much bite your head off if you answered a cost question with
something like "Oh, not too much" or a timeline question with
something like "a long time". She would very quickly let you know that
plans and decisions can't be made based on answers like "pretty soon"
or "very expensive". Specifics were required. The whole project team
would cringe when a newbie tossed out an answer like that. We all knew
what was coming next.)