What would replacing the whole system entail/do? Other new parts? Something to your house? Cheaper bills down the line?

Keeping some of that stuff off standardized tests seems like a kindness -- avoiding bringing up outside trauma in an already-stressful situation. But birthdays???

I take it this is an air-source heat pump, not a ground source heat pump.

HOWEVER. Since sj is buying a house, I want to say, I have never regretted buying instead of renting. When something breaks in my own house, I can just get it fixed. Negotiating with my sister is nothing compared to wrestling with a reluctant landlord.

Why do I have to consult my sister? Because she's part-owner of the property, and joint owner of the bank account the savings is in. I could just do it without asking her, but it would upset her if I did, and rightfully so. She has a say in it.

A quick Google found this on Trane heat pumps. [link]

Don't know how representative this is, but at least your sister is not basing her dislike of Trane heat pumpos on nothing. Don't know if these are outliers rather than typical.

I take it this is an air-source heat pump, not a ground source heat pump.

I don't know what that means! There's an outside unit and an inside unit (the condenser, I believe).

Argh. I am soooo tired. Want to go home. . .

What would replacing the whole system entail/do? Other new parts? Something to your house? Cheaper bills down the line?

Since this system is old, parts will keep breaking. Replacing it now means less hassle and maybe less expense down the line. Replacing it will also probably lower my electric bills a bit, since a new system won't have to work as hard as the old system apparently is.

Don't know how representative this is, but at least your sister is not basing her dislike of Trane heat pumpos on nothing. Don't know if these are outliers rather than typical.

You know, no matter what the thing is, some of them are going to suck, and some of them will be superlative. You can find complaints on the Internet about everything. Not that it's nothing, but I can't base my decision on a handful of complaints from strangers.

It really doesn't make sense to just replace the compressor. Today's models will be at least 30% more efficient. What's your electricity supplier?

(I'd be happy to talk you through it. I've written way too many articles and brochures about heat pumps.)