Gradually assembling a mk 2 S - up to fitting the heater unit.
It has never worked well (or not at all) in the heating department.

My mini K has a mk1 heater fitted and it's like a blast furnace, so I'm wondering if the Mk2 heater (moulded plastic body rather than the metal Mk1 version) has a design problem which other owners have experienced, or it's just the matrix needs a good flush?

mine is good .. toasty feet in winter

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did I tell you that I won a trophy?

It's probably full of crap like my son's Clubby one was. Backwash fixed it.
If it's got an alloy tap on it? like a Clubby does they corrode to bits.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Mine has two settings. Off and Flay.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I'm slowly soaking the heater core in a solution of Barsleak granules, between blasts from the hose to break up the crud.
The heater didn't work much before this, so there's not much riding on trying to fix it now.

Yeah, if the flow was good and the water was obviously hot, I would think the fins would be coated inside with old scale or blocked. Although you are likely not looking at replacement just now, I am probably wrong, but I thought Mk1 heater matrices fitted Mk2 plastic cases as well?

https://www.minisport.com/17h8608-heate ... 64-69.html

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I also assume that both heaters used the same core.
The outside of the fins look to be a bit rusty and dirty, so might be worth a wash too.

Worth giving the heater tap a close look too.

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Cheers Dave.

The tap on the head is new. The engine hasn't run yet. Just know from experience that the heater has always been ineffective, so there is more chance I would try to fix it while it's off the car.

So historically the tap is not the problem. That being said there may be some swarf or crud from sitting that ends up in the tap at a later time. Just a heads up.

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Cheers Dave.

Hope you don't think I was dismissing your suggestion. All thoughts are welcome for consideration.

Not at all, just giving the benefit of previous experience to limit the prolonged head scrathing that accompanies mini ownership.

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Cheers Dave.