Since about last week, the temperatures went really down to around freezing point, and my Dad complained to me that he seems to always be cold in the house, and when he raises the thermostat setpoint a few degrees, he doesn't hear the oil burner firing like he used to with the old thermostat. I was there last weekend, and noticed that the heat pump is often in defrost mode, like 10 mins every 45 mins or so, and when it is in defrost mode, the oil burner doesn't kick in. Could it be just due to the fact that the heat pump is 21 years old, with the original compressor, or could this mean something's bad with the controls?

Also, if the house finally gets to the desired temp, if he raises the temp, even by 10 degrees, it takes about 2 mins for the furnace and heat pump to kick on, which we find strange. Same delay with the emergency heat button.

Here's the catch:
the guy gave my Dad a quote of $550, but when the work was completed, he wanted $875! He said it's impossible we gave you that low price of $550 over the phone, blah blah blah. The guy who showed up seemed like a novice, he was about 20 years old and needed to read the instructions for the thermostat for about an hour before proceeding, constantly checking his work with the installation instructions (which he took back with him). The whole operation took about 5 hours. My Dad felt like he got ripped off and called his boss, who finally agreed to bring the price down to the original $550. When my Dad called the company again to come and check why the oil burner doesn't fire up, they said "we don't go to your ****** house anymore" and they hung up.

Now my Dad tried to call other companies, but no one wants to touch "other's people work". I have a degree in electronics and controls, and that's what I do for a living, but I have absolutely no experience with HVAC systems. Would someone be kind enough to help me troubleshoot this situation myself? I am very good with electronics and electricity, and I am confident that this is something I can fix if I know the basics like what calls the oil burner while the heat pump is in defrost mode. To help you diagnose the problem, I have opened the interface box and the guy replaced the old board (which was just a PCB with a big block of black epoxy and some terminals) with a cluster of relays, a transformer and some wire nuts and electrical tape that really look like a hack job to me. The guy also said he replaced the contactor in the heat pump "because it was on its last legs" but I haven't looked there yet so I don't know what he's done in the heat pump cabinet. Any help would be greatly appreciated, and thanks for taking time to read my long post. If you want, I can take pictures.

Next - if you didn't get a written quote, challenging this after the fact usually turns out in the way it happened to you. You should always get a written quote before the work is started. But it's too late for all that now. Just something to keep in mind for 'next time'. I'm not surprised you got fired as a customer. I see that happen all the time.

Now - my next thing would be that if they forgot to install the duel fuel kit - did they also forgot the outdoor thermostat (probably). I would make sure that is installed. The next thing is to download the installation manual and start reading (then you'll also get an idea of what the installer goes through). Make sure you are looking at dual fuel application. It sounds like a jumper may have been missed or not cut. It sounds more like a wiring issue than a programming issue - but I'm no thermostat pro. You need to make sure the setpoint to kick it over from heat pump to the furnace is set where it should be. Depends on where you live and what sort of comfort to energy efficiency you are more worried about.

The best advice as a starting point is certainly what ziggyhere suggests. Download the installation manual. You are knowledgeable so as you read it, you'll become familiar with the control and the devices it controls. Where you might have a problem is where some of the controlled devices are located and what they may look like. A lot of good guys here and are willing to help.

However, I couldn't find an exterior thermostat as ziggyhere mentioned, but the heat pump's wiring diagram shows a temperature sensor; could the old system have used that as the outdoor thermostat? If not, my parents are on a dual rate from their power company: they get a discounted rate as long as the outside temp stays above -12 degrees Celsius or around 10 degrees Fahrenheit. The power company installs a temp sensor in a housing that mounts between the meter pan and the meter itself, with 24 VAC present at the furnace when the temperature is above the setpoint of 10 degrees. Could the old system have been using the signal from the POCO sensor to shut off the heat pump and switch to oil? Also, when the temperature outside was around 16 degrees Fahrenheit, sometimes the oil burner would come on for a couple minutes (and the heat pump would shut off), and it doesn't do that anymore; could that be a feature of the old system, or could it be a feature of the heat pump itself? Also, with the old system if we raised the thermostat's setpoint even by a few degrees, the oil burner would kick in until the desired temperature is reached, but the new system doesn't do that; is it typical of dual heat systems, or was it just a feature of the old system and I shouldn't worry too much about it?

Finally, I have heard and read several times that below a certain temperature, heat pumps lose their efficiency and there was indeed a chart in the heat pump cover, but after 21 years out there, it isn't legible anymore. It's an ICP 2-ton unit, if that matters. Because the system would often rely on the oil burner past the 16 degree mark, I assume that is where that particular heat pump starts losing its efficiency. Is it putting more strain on the compressor to let it run below that threshold?

Thanks again for taking time to help me, and have a nice day!