We just recently bought another house, and I'm having some problems with the heat pump in heating mode.

We've got a Lennox HP25 411 1P heat pump as well as a 1 year old Carrier oil furnace which is acting as the air handler. We've also got a Lennox fuelmaster 21 as the fossil fuel kit(no outdoor thermostat is hooked up to it).

Anyway, the heat pump is noisy in the heating mode. In cooling mode, the heat pump is quiet; but in heating mode, it starts out rather quiet; but then gets louder and louder.

From the outside, I haven't really noticed an increase in noise, but you sure can hear it on the inside.

The heat pump also will stop heating, but the furnace fan and the condensor fan will keep running.

I have turned the thermostat off and left it off for a half hour or so and then turned it back on which caused the oil furnace to come on(the temperature in the house must have dropped enough to call for the emergency oil heat).

When the oil furnace satisfied the thermostat, the next time the thermostat called for heat, the heat pump started working again(although it still gets noisy).

The heat pump seems to stop heating when it's being asked to run a long time.

I've noticed also that it will eventually start heating again even if I don't turn the thermostat off. It just takes a real long time(like a half hour or more).

Anyway, what would cause a heat pump to run fine and quiet in cooling mode and then become noisy and sometimes quit heating in heating mode? Would a clogged up filter drier cause this or how about a defrost problem?

I didn't see a TXV.

I can live with the noise, but I don't really like the unit not heating except maybe when it's in defrost mode. Come to think of it, I don't think I've ever seen the thing enter defrost mode. Maybe it's too warm outside, or maybe not...

Thanks for any replies.