Heat pump shuts off quickly

[dmanmtl]

Hi,

I have a Gas furnace and 2 ton Lennox heat pump. The heat pump is almost 2 years old and the gas furnace is a Heil and about 10 years old. I will call a tech to come and look at this problem but I would like some guidance so I know if he is onto the right problem or not.

Here is the issue: The heat pump will not run for more than about 20 minutes, then the gas furnace will kick in - the temp drop is not the issue, the heat pump seems to heat well, nice warm air. I changed the thermostat thinking it might be the problem but it has not helped. It's not too cold here, the thermostats is set to call for heat when the temp drops by 1C.

Any idea what could be causing this I was sue it was the thermostat). My main issue is that the heat pump is still under warranty but I don't want to call the company that installed it to check this problem (long story) but they will have to fix it if it is a warranty repair.

Thanks in advance!

[Sonicview]

it could be a number of things but initially what comes to mind is if you had setback your thermostat at night by more than 3 degrees and by morning you called for heat... your heat pump would kick in first then your aux heat being your furnace would have kicked in...once the temp comes up, the heat pump should take over the next cycle unless the thermostat is set to lock it out and it got cold enough in your area for it to do so... hope this makes some sense to you...

[beenthere]

Could be several things.
But with the limited info you gave too much guess work.

[dmanmtl]

I don't think it is an issue of the temp getting too low and then needing aux heat to catch up...and I am not referring to just in the AM - I have not been using the setback program - we just leave it at 20C all the time.

If I move the thermostat from 20 to 21, the heat pump comes un, runs about 20 mins then I hear the gas kick in (just did this) but I am sure that if the heat pump had run a little longer it would have caught up to 21.

A couple of questions for you knowledgeable guys:

1) Is there some feedback mechanism between the heat pump and furnace/thermostat that allows the heat pump to basically say: "I am done, can't go on any longer - Gas: you take over" - because of soem defect in the heat pump?

2) Is there a time limit on how long the heat pump will run before the gas is called for - I thought this would be controlled by the thermostat but I see nothing about this in the docs

Thanks again - I like to know as much about these things before the tech guy gets here.
D

[dmanmtl]

posted twice by accident

[beenthere]

Yes, the HP, furnace and stat are interlocked.

What thermostat do you have, brand and model. And is it the same brand and model as teh old one.
What is the outdoor temp when it does this.
How long has it been doing this.

[dmanmtl]

Yes, the HP, furnace and stat are interlocked.

What thermostat do you have, brand and model. And is it the same brand and model as teh old one.
What is the outdoor temp when it does this.
How long has it been doing this.

I installed a Honeywell RTH7400, I had a cheap White Rogers before this one.

Its about 50F when this is happening, not cold enough to need gas heat, in my opinion.

Thanks for your reply!
D

[Sonicview]

did you go through all of the menu setup options when you installed the tstat? Did it ever work with the old thermostat? There are so many options on the tstat and all of them are important to choose correctly for your system to operate properly.... in order to set up the tstat correctly you need to know what type of equipment you are programming the tstat to operate... ie... single or 2 stage heat pump? single or 2 stage furnace? outdoor temp sensor? reverse valve power needs, etc.... you may want to call your service tech to check it out,

[dmanmtl]

did you go through all of the menu setup options when you installed the tstat? Did it ever work with the old thermostat? There are so many options on the tstat and all of them are important to choose correctly for your system to operate properly.... in order to set up the tstat correctly you need to know what type of equipment you are programming the tstat to operate... ie... single or 2 stage heat pump? single or 2 stage furnace? outdoor temp sensor? reverse valve power needs, etc.... you may want to call your service tech to check it out,

It's a single stage heat pump and single stage gas furnace. not outside temp sensor aside from the hydro company switch that shuts it off at -12C(dual energy system).

I am planning to call a tech just not sure if its a heat pump problem or something else. The heat pump is under warranty with one company but I don;t want to call them if it is a furnace or tstat problem as they do not service my type of furnace (but still charge a hefty sum to come out and loo at it)....

Any suggestions what could cause this problem?
D

[beenthere]

You have a dual fuel system.
Do you have a seperate dual fuel control.
Was your old stat a dual fuel stat.

Might be a problem of the wrong type of stat.

[patrick]

Where is this "hydro company switch" located?

It could be getting cold air blown on it from the heat pump and turning off early.

Some t-stats do bring the furnace on if the heat pump is taking too long to heat the house.

[dmanmtl]

It's on the other side of the house.

And the t-stat is made for a dual fuel system - one of the options in the setup was to select the fuel options - it is set to the correct combo...

Any other ideas guys?

[beenthere]

What option number did you select.
I don't see an option for dual fuel for the RTH7400.

[dmanmtl]

What option number did you select.
I don't see an option for dual fuel for the RTH7400.

In option 0170 I set selection #7 - Heat pump with backup aux heat

Make sense?
D

[beenthere]

That just tells it, it has aux heat.
Some heat pumps don't have any aux heat.

0170 set to 7, doesn't tell it that its on a dual fuel system.

With that stat, you need a dual fuel control also, for dual fuel systems.

Wrong stat for your application.

[dmanmtl]

That just tells it, it has aux heat.
Some heat pumps don't have any aux heat.

0170 set to 7, doesn't tell it that its on a dual fuel system.

With that stat, you need a dual fuel control also, for dual fuel systems.

Wrong stat for your application.

My system also has a dual "fuel control board", including a changeover relay that switches it to GAs only when the temp drops below 12C.

[beenthere]

12°C is 53°F. So thats why its able to go to gas heat. The dual fuel control is set too high.


Since the heat pump should be able to keep up at 50°F outdoor temp. It may have a problem with the refrigerant charge. Or the coil could be dirty.
So teh stat is sensing a loss in temp, and bringing on teh aux heat.

[dmanmtl]

12°C is 53°F. So thats why its able to go to gas heat. The dual fuel control is set too high.


Since the heat pump should be able to keep up at 50°F outdoor temp. It may have a problem with the refrigerant charge. Or the coil could be dirty.
So teh stat is sensing a loss in temp, and bringing on teh aux heat.

Apologies but I meant to say -12C - that is the temperature at which our hydro company starts charging more for electricity so the heat pump goes off when it hits that temp.

Thanks so much for your numerous replies! I really appreciate your help!
DM