Quick update.

I ended up buying a full LR replacement unit in the end, plugged it in and works perfectly.

I’m sure the repair option is not impossible if the pettier cell is the correct size but I think squishing mine in as it was slightly too big probably killed it. 2007 Range Rover L322 TDV8 Vogue SE (Rimini Red)

Just replaced my seat back unit, got a nice toasty back and bum now, woohoo!
Bit puzzled though as there is absolutely no sign of damage to the plastic duct housing, the fan runs fine and when on cooling it works perfectly. I switched it on to heat with only the back unit lit on the button and it runs when on heating, but only blows cold air out. Thought I may have to replace the seat base as well, as when on back heating only apart from blowing out cold air the IID tool didn't register any faults, but if I then switched on the base heating using the button it ran for about 10 seconds then cut out totally and a fault was flashed up. As soon as I put the new back unit in and ran it, all was well, both back and seat base gets warm. Strange.

I didn’t need to remove the seats to get the seat backs off. I moved the side trims away by removing a few screws from the side trim undersides the manipulated the seat back down the way whilst unclipping the bottoms of the seat back from the seat

That picture show the heater blowers hanging out of the back of the seats after I removed the three screws and the two zip ties holding it to the seat frame

Thanks to Downhill & his thread, this spurned me into action & removed the back heater unit. Nowhere near as complicated as I thought it was, no need to remove the complete seat. Motor was out inside 30 mins which I thought was pretty good for a ham-fisted 63 year old! Just need to order a new one from Duckworths & all being well, a warm posterior........providing the reason for seat base failure was this.............

Click image to enlarge

Who's got a nice warm bum & back?
Fitted the new rear heater unit this morning, plugged her in & heated drivers seat base & back........lovely.
I was concerned about doing the job, but, having read so much on here decided to give it a go. It wasn't that bad, really.
Thanks to Rob at Duckworth Parts for his help, super quick postage & a very impressive cost for the part, £276.14 all in.

Click image to enlarge

If the driver and passenger seat back units are identical, I might swap them over - then my wife can have a cold arse rather than me  Pikey by name, not by nature

Just to piggy back off this.
Earlier this year I repaired the ducting in the seat back of mine.
The base worked fine but the back never got warm. The repair worked perfect.

Now weekend just gone it’s all stopped working.
Did some investigation today and it powers off after 30 seconds or so.
Error code - B1231 7A

Would I be right in thinking this is the base unit at fault now?

JNC:
B1231-7A [Right seat fluid leak or seal failure].
I had this on my drivers side seat, no heat from the base nor back, and, like JNC if you stick your ear near the base of the seat, the fan ran for 20-30 secs then stopped.
It was a bit of a gamble changing just the heater unit on the back of the seat, but consensus of opinion says that's the one that normally plays up.
There is a similar heater unit underneath the base of the seat but there's little evidence on here that this plays up.
Finicky things these RR seats and pardon the pun.....a right pain in the arse!
Hope this helps. 2012 Orkney Grey Westminster 4.4TDV8 with Ivory interior.........nice!
Alfa Romeo Giulietta
Just one Montesa now, 349 White Wonder
Austin A40 Farina MK2
1975 Morris Marina 1.8TC
1973 Honda CB250 K4

I thought there was a different fault code for the seat back part?
I have previously repaired the seat back ducting as only the base was getting hot.

But now there is nothing, it powers off after 30 seconds.

When the LR Indy put his Autologic Code reader on her, it came up with this:

B122F-28 Right seat back. Component or system is over temperature
B1230-98 Left seat back Component or system is over temperature
B1231-7A Right seat. Fluid leak or seal failure

The last code omits the word 'back' so I wonder if that just refers to the 'base'?
I have to confess I haven't tried the new motor on 'cool' yet, to be honest, I don't think I'll use it so not bothered either way, it was the heated bit I wanted to cure.
There is another heated motor under the base, slightly cheaper by a few pounds.

Again, hope this helps. 2012 Orkney Grey Westminster 4.4TDV8 with Ivory interior.........nice!
Alfa Romeo Giulietta
Just one Montesa now, 349 White Wonder
Austin A40 Farina MK2
1975 Morris Marina 1.8TC
1973 Honda CB250 K4

I've done a lot of work to get faulty back or base units working to not avail.
I plumped for several replacements and this tends to sort the error codes best!!
I'm loving the warmers as this weather starts to turn, don't delay!

There is one story I've read (is it above somewhere?) of a guy repairing his with an alternate and cheaper unit, have a search.

. Cheers, Greg
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2011 Vogue SE 4.4 with lots of toys in Stornaway

I have found someone selling just the peltier part on eBay. About £70 imported.
Can’t believe there isn’t another source for these.

sure but see up a page or so - member michaelpalmer7 found one, fitted it and it didn't work.

tried a Ford US unit myself (from a Mustang) and it didn't work
. Cheers, Greg
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2011 Vogue SE 4.4 with lots of toys in Stornaway