Honeywell Controller keeps turning the Burner off.

JAdams

Olsen HDS-90T (Direct Vent) Forced Hot Air Condensing Furnace. New Honeywell S9200U1000 Universal Control Board. Problem: The controller keeps shutting down the gas valve. The code clearly points to an air flow problem (obstructed heat exchanger, not enough return, air filter, etc). There is problems with the ducting and the returns that need to be addressed, with out a doubt. However, the unit still shuts down on the same code with the blower door completely removed (all the return air it should need and then some) and the end cap of the 8" x 20" Duct completely removed and the fan speed on high. The more I opened things up, the longer the controller would hold, but eventually lock out. I would have thought that with both items removed, there would be plenty of air flow, however I was wrong. The heat exchanger if free from obstructions and any dirt. Fan motor turns the proper rpm. There are only two remaining possibilities, that I can think of, as to why this keeps happening: 1) bad controller, or 2) BTU output is too much and needs to be lowered (which, to me, doesn't make much sense because of the ducts being wide open (not to the point where it will do damage to the heat exchanger), and the air flowing like the winds of a hurricane). One thing I almost forgot to mention is that the furnace is in a confined space: about 300 sq ft area. One thought I had was to knock down the the BTU's by changing the burner orifice's to the next smaller size. But before I do that, I'd like your opinions, please.

unclejohn

The board shuts the furnace down because the limit tells it too. You need to check the temp rise through the furnace after you put everything back. That will be your starting point. normally 70 - 100 rise is ok. That info should be on your rating plate. If you are with in the range and it trips out you need to check the temp at the limit. If its lower then the trip point you have a bad limit. If its higher you could have a bad heat exchanger.

JAdams

unclejohn said:

The board shuts the furnace down because the limit tells it too. You need to check the temp rise through the furnace after you put everything back. That will be your starting point. normally 70 - 100 rise is ok. That info should be on your rating plate. If you are with in the range and it trips out you need to check the temp at the limit. If its lower then the trip point you have a bad limit. If its higher you could have a bad heat exchanger.

Thank you for the reply Uncle John. You know, when writing these things, I try to be specific as I possibly can, however, I always tend to leave out some details. One of these days I'll get it right.

Tim McElwain

There may also be an auxillary limit in the blower compartment that is sometimes a heat assisted limit and will shut down to protect the heat exchanger from thermal stress.

Where is this unit getting its air for combustion, I assume it is from outside if so what does a confined space have to do with the problem.

Why was the original Integrated Furnace Control changed? Was the Universal replacement properly cross referenced as a replacement?

JAdams

Thank you for your replies. The problem is definitely air flow! I went back to the site on Monday, one day after the owners had left, to measure for a heat loss calc. They set back the TT to 45F when they left. It was indeed 45F inside. I took my measurements and decided to check that furnace one more time. It ran perfectly, without locking out. Of course the blower door was still removed. I was able to do a temp rise test, which fell in between the manufacturer's specs. Once I replaced the blower door, the output temp increased to 140F and shut down on high limit. Removed the blower door again and it ran like it was supposed to. The return air was cool enough, with the return door removed, to let that furnace do it's thing. Once the house comes up to temperature and the return air is 20-25 degrees warmer, the output temp rises (obviously) and the unit shuts down on high limit. So, the unit and controls are working as they should, it's just not moving enough air. More supplies and returns are needed for the unit to run properly at room temperature. I'll still do a heat loss on the house to find out exactly what it needs for BTU's and for reference.

Once again, thank you.

icesailor

Many scorched air systems installed today suffer from severe cases of COPD. Amazing what you can tell with thermometers on a heating/cooling system.

And how long they run all FU'ed before a smart guy like you comes along and doesn't start picking at "Air Answers".