I'm not sure if you have enough information to expand on your description @delt ,
but why is it that brazing/welding/soldering would be required?

Is the nitrogen to facilitate that brazing in an oxygen-free environment, or because it's required to flush out the existing refrigerant?

Thanks for the immediate reply. Short answer is I do not know - these are line items on the quote I have (I guess I should go back and ask for clarification). All I really know and understand is that the compressor unit has broken beyond repair  and needs replacing - the company has listed these things as part of the job. Perhaps we should not get too distracted by the nitrogen & brazing materials since they are <3% of the total quote. I was hoping for some ball park estimates/range for comparison, but perhaps its not that easy?   

Posted by: @transparent

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why is it that brazing/welding/soldering would be required?

When brazing copper refrigerant pipes, nitrogen is passed through the pipe to prevent oxidation (contamination) of the inside of the pipe, if I understand it correctly.

OK. So we assume that the compressor can't be fitted using copper pipe connectors.

@delt - can you please tell us the GSHP manufacturer and model number?
We'll then be better able to assess the component price.

The compressor is brazed to copper pipes - brazing is basically much higher temperature soldering, joining copper pipes together with a dissimilar metal (often high Silver content).  It's stronger than soldering, which is important for the longevity of the compressor as it spends it's life vibrating.  Starts and stops are especially abrupt, and cause fatigue on the joints.  Often the whole lot of the heatpump is brazed, but so long as the pipes are long and have enough bends to absorb vibration, it's the compressor ones that really need it.   

They'd have to vacuum pump the refrigerant out, safely store and likely dispose of it.  Put nitrogen in the system.  Cut the old compressor out.  Bleed nitrogen (or other inert gas) through while brazing a new one back.  Ideally swap out the dessicant filter (water reacts with compressor oil to form acid, kills the compressor).  Vacuum again, check vac. maintained, refill with correct gas weight.

@transparent Ok so I intentionally did not include the manufacturer/model/ since they are sole supplied in the UK and I do not want this to become an exercise in highlighting the prices of a specific company. Without this info perhaps my ask is unrealistic, in the way that quotes would wildly differ for engine work on a Ferrari vs Ford. Maybe  I should rather pose a more general question to owners of midsize (eg 10.5kw) GSHPs  as to 'how much did you pay/would you expect to pay' if you woke up tomorrow and your compressor had failed? <£1k, 1-2K, 2-3K, 3-5K, >£5K?? Suffice to say I had an unpleasant surprise when this happened to me - I have not really seen these costs/risks baked in to GSHP ownership so looking to raise the question and awareness. Hope there is sufficient for you to punt a range but understand if not - many thanks for the comms

@robl Thanks - thats really helpful and much appreciated

No, that's quite understandable @delt

Most ASHP models share common internal components, often across different manufacturers.
If you know what you're looking for, then you can buy almost anything you want directly from a Chinese warehouse on AliExpress.

GSHPs are different.
The very nature of the design means that they can't "borrow" components from the Air Conditioning market.

As I'm in West Devon, about 4 miles from 'the border' I took time to go and visit Kensa, who make GSHP units at the far end of Kernow.

They only manufacture GSHPs (no ASHPs) and they have a brilliant team of in-house design engineers.
I would certainly feel very happy buying into that product-range.
But I'd be very careful who I chose to install it.
There's no point investing in a well-engineered product unless it's also installed by someone who really does understand the system.

The downside of course, is that the sole source of replacement parts would be Kensa themselves.
For that reason I'd be looking at the feasibility of long-term maintenance contracts and/or insurance.
I might even insist that firmware upgrades were included in the package.

I would also want to have a control system which permits remote monitoring.
That would allow the installer, or Kensa themselves, to see how the pump is behaving without me paying to bring someone to site.

I don't yet have a heat-pump.
But I'm on the same piece of granite which allows Kensa to dominate the market which they've grown in SW England.
They don't need to advertise. Almost everyone buys on their reputation.

And part of the attraction is that there are several drill-teams who can sink boreholes in the area.
The legacy of Cornwall School of Mines at Camborne has given us some benefits not enjoyed elsewhere.

So I too am interested in hearing of the situation in which find yourself.

... and at this point I strongly suspect that @editor will move us off the Welcome Topic and into our own thread. Stand by!

@delt I liked to make a stab at this, so some of the things to consider:

engineers travel time to site,

say 1 hour @ 65/hr

engineers travel time back home, again 1 hour

8 hrs on site @ £65/hr ( prepare, vac down, remove old compressor, fit new compressor, pressure test with nitrogen and hold, fill with refrigerant, run up and re-commission) 

R407 scroll compressor £560+ carr £12

new dryer/filter £25

refrigerant gas £25/kg assume 2.5 kg system charge 

sundries @ £40

total approx. £1600 inc VAT.

I'm sure you'll let me know if I'm close or off by a mile. 😁

Those labour charges look low to me @iaack

An engineer with the training, skills and equipment to undertake this work will have substantial overheads to meet.

@transparent You could well be right. Current salary for a refrigeration engineer is in the region of £40k per annum ( £20/hr.) Cost of training tools van and other over-heads recouped by their employer, hence my stab @ £65/hr.(+Vat), but it could be nearer £85/hr

Difficult access to the compressor for swap out for instance will create extra work. And no doubt ideal time to carry some routine maintenance work on the system will mean potentially an extra day on site  (extra £700 to budget).

@iaack Thanks all for your insights - its really much appreciated. Ideally I would have heard from someone that had first hand experience of having their GSHP compressor replaced but I guess these people are relatively few and far between. Anyway, to round this out, the total quote for my repair is £3.5K - the new compressor was £1730, labour/travel £1330 and the rest in sundries. Labour rates charged at £60ph. My purpose here is not to complain about the cost - it is what it is and I have no choice. Rather, its to flag to others the reality of potential repair bills that could be around the corner. Lets just say it was a v unpleasant surprise!

My bigger concern is that the new compressor and repair work is only warranted for 12 months - in theory I will have the same risk exposure this time next year with no means to warrant or insure. That doesnt make we sleep well at night when the only other option is a completely new pump (>£10K). Indeed, I was trying to think of anything else in my life where I could wake up one day to such a pressing, costly bill that I couldnt otherwise have warranted or insured???  @transarent raised a good point about long term warranties or inclusive service cover which I wish I had the option to buy into.   

Thanks again 

The guarantee on a compressor is surely worth more than the £3.5k repair quotation?!

If you can't get a reasonable guarantee for having the manufacturer-approved part fitted, then you might as well buy a really cheap GSHP elsewhere and expect to replace it every 4-5 years!

I realise that these are not like-for-like comparisons, however

1: Here's a company in Poland who manufacture GSHPs and sell on ebay at £1900, so long as you arrange collection.

2: Also from ebay, here's a brand new Dimplex GSHP being offered at £1500; pickup from Swindon

3: I can import a 10.5kW GSHP from China via AliExpress for £5558  plus £1338 carriage:

Or do 2 minutes extra detective work and buy the identical model direct from the Chinese manufacturer on Alibaba for £1379 + carriage (negotiable)

And it doesn't take me too long online to find several workshops that refurbish scroll compressors (usually in the Midlands).
They'll sell you one for £300, and arrange to come to site and fit it if you pay cash! 🤔 

Sure, none of those options have a warranty of any useful value...
... but there's a better than even chance that they'll last longer than the 12month warranty you get by using an 'official route'.

@delt wow!  How old is the system?  This is why I took out the 10 year fixed price service and warranty on my Daikin ASHP. To cover such eventualities. 
Best wishes with your fix