Zoned HVAC system short cycling on 2nd stage

logan1211

Hey all. Hoping someone can help me a tad and offer some input. I’m pretty handy and have been digging in to this issue a little more. We had been fleeced by our previous HVAC folks. And by fleeced, I mean, assumed they’re competent.

I’ll try to be brief.

We have 3 zones. Heat pump, and 2 stage gas furnace (propane) - brains is a NCM-300 panel from EWC. Pretty basic setup. There’s also a barometric damper between supply/return but it’s only like 2’ from where it leaves the furnace and 2’ before it returns.

I noticed some short cycling recently and was like, crap, forgot to clean this out in September. So I cleaned the A coil, blower, replaced filters - all good! Or so I thought..

When running for an extended period of time (big temp rise called for on thermostat for example) after 5-8 minutes after 2nd stage gas furnace kicks in, high limit trips and shuts off.

I turned all heat to emergency mode to only use the gas furnace, same exact behavior.

I have some questions while I’m trying to find a reputable and competent with zoned system HVAC company...

With a heat pump and 2 stage gas furnace. Where does the logic exist that determines when 2nd stage gas comes on? Wondering if that was “tweak-able” there is a w2 staging timer on the control board; but I’m not sure if that’s time that heat pump runs before kicking over to gas?

Is the barometric damper garbage? Should I be looking at a “modulating bypass damper?”

Efficient or possible to disable 2nd stage gas completely if first stage can keep up without running 24/7?

Ultimately I surmise I’m either not moving enough air across the heat exchanger, furnace is oversized, or something else I’m not thinking of... we’ve been in the house a few years and it’s very possible it’s been doing this the whole time and we’ve only recently known about it.

ratio

The manual for that zone panel shows both a 2nd stage heating timer and a high temp heating limit. The timer controls how long the unit stays in stage 1 heating before calling for stage 2, and the high limit tells the system to stage down the heat. I believe you will need a supply air sensor to use the high limit setting. If you are using two stage thermostats, lift the second stage wires from the control board to allow the panel to control second stage. Set the heating limit to just at or slightly below the point where the furnace limit switch trips. You will want to fiddle with the staging delay to give the calling zone a chance to satisfy before staging up or another zone to start calling.

GBart

Agreed, you need the manuals and the board should be calling the shots not the t-stats, you shouldn't be going into 2nd stage on one zone, and as stated without the temp sensor the zone board is blind.

Your furnace board may also be set up wrong, they have options, it sounds like it's in the timed option where after 5 minutes run it goes into Hifire, that will have to be changed AND the must be wires running from the zone board to W1 and W2 on the furnace.

logan1211

Thanks all. I'll dig more into these suggestions later.

All thermostats are single stage to the board.

I do have the Supply Air Sensor off the board in the supply duct; but all that does it shut heat/cool off if that specificed temperature is hit. I suppose I can dial this down, to shut gas off vs. high limit doing it...Probably a little easier on the unit?

That timer though, if you're referring to the one on the control board, is how long the heat pump runs before gas furnace kicks in. Then from what I'm understanding there's a timer on the furnace that after X minutes, gas furnace will go in to second stage/hifire ...and that's where I'm high limit tripping (after 5-8 min or so of second stage gas running)

Time to do some more reading through the furnace manual You guys are great - thanks!

John Mills_5

Zone panels have differing ways to stage the gas heat. Is the zone panel doing dual fuel or is there a separate dual fuel kit? Not familiar with that panel but I'm not sure it can do 2 stage gas backup and dual fuel. But what the guys are saying is that that zone panel can downstage when the air gets too hot. Is there a high limit setting on the zone panel that is set too high?

logan1211

Hey John, there is a high limit on the zone panel. But according to the manual, this just shuts down the heat when that limit is tripped and blows the fan for 3 minutes...then restarts if thermostats still calling for heat.

It looks like this zone control board just acts like a "single stage" thermostat to the furnace control board and that the gas 2nd stage/high fire is just time delayed.

It's dual fuel, from a W1 = heat pump, W2 = gas standpoint...the staging timer then kicks on W2 after X minutes (potentiometer dial on the board that sets that time)

GBart

That's your problem, the zone board should be controlling the unit from a W1 W2 standpoint and the board on the furnace needs to be reconfigured, the thermostats can stay with just a W wiring, so if one zone calls you're on low fire, if two call you go up to high fire