I read a comment, I think in this forum, a few weeks ago that GSHPs and radiant systems can be costly to maintain. The comment was something to the effect that one guy makes a good deal of money with maintenance contracts on GSHP and hydronic systems.

I'd like to know, in general terms, how costly heat pumps and hydronic systems are in terms of maintenance, particularly typical lifetime of a system and frequency of replacement. Let's leave out the water/refrigerant heat exchanger and water quality impacts on water source heat pumps. If I go with GSHP it'll be direct exchange, not water source.

An HVAC distributor I was talking to the other day said GSHP heat pumps are fairly limited in life, and have to be replaced every few years. Air source heat pumps in years past had a not too good record for reliability, but they're a lot better now from what I hear.

Soooooo, what's the real world experience of the past 10 - 20 years?

This is a  typical response from someone who wants to sell a furnace.  The truth is that longevity is one of the selling points of GSHP's.  The useful life is 15 - 20 years. About all you have to do change the filter on a regular basis.  With a DX system there might be some kind of periodic checking needed on the refridgerant level.  

Actually, he's not pushing a furnace. This is the guy who distributes the Daikin heat pump system I mentioned in an earlier thread!

To the OP, I'd be interested in hearing someone's experience in this regard as well.  Sure hope this thread lives on...many other promising posts here seem to have similiarly fleeting lifespans.