Heat always on

relistan

Member
I have just started to research possible causes for this issue, but thought I'd post here as well in case someone has a quick answer. I did search but didn't see any threads that looked like a clear match.

I understand that the heater box is running all the time in the P6 normally, however, I don't seem to be able to prevent it from heating the cabin in my car. The levers on the dashboard don't appear to have any effect. I think I may need to have the thing out, but I'm hoping there might be a simpler cause that someone can identify.

Any ideas?

Thanks,
Karl
 
Correct, the heater matrix is always connected. The temperature lever controls flaps that either direct air over matrix or bypass it depending on whether you want hot or cold air. The insulating strips on the flaps do fail, but the usual symptom of that is no heat, not heating always on. Maybe the linkage from the lever to the flap has become disconnected? If you get someone inside the car to move the levers, you should be able to see the linkages on the outside of the heater box moving. If they don’t move something is disconnected. If they do move then you’ll have to investigate a bit further into the heater box.
 
Correct, the heater matrix is always connected. The temperature lever controls flaps that either direct air over matrix or bypass it depending on whether you want hot or cold air. The insulating strips on the flaps do fail, but the usual symptom of that is no heat, not heating always on. Maybe the linkage from the lever to the flap has become disconnected? If you get someone inside the car to move the levers, you should be able to see the linkages on the outside of the heater box moving. If they don’t move something is disconnected. If they do move then you’ll have to investigate a bit further into the heater box.

Ah, excellent. I will do that. I had not gotten so far as to realize the linkage was visible in the engine bay. Thanks
 
The levers on the outside of the heater unit can move, but that's doesn't mean that they are moving the flaps inside, they can just turn on the shaft.
 
The bits that move flaps are on the left side of the heater casing. If you drop the pass side storage bin (shin-bin?) you should be able to see where the heat control levers connect to the heater box arms.
 
The heater looks like this when removed and if you look at the rear of it, you'll see two 'forks' which your controls inside the car bolt onto. The three levers on the side of the heater can be seen from under the bonnet, from the left hand side of the car, so if you can get someone to move the controls when you look at these, they lower two should move to move the flaps.

If they don't then the usual problem is either they have come undone from the inside, (easy fix) or the the splines have gone (not easy fix :confused:)

heater control.JPG

Inside view from left hand of car.

heater controls.JPG
 
The heater looks like this when removed and if you look at the rear of it, you'll see two 'forks' which your controls inside the car bolt onto. The three levers on the side of the heater can be seen from under the bonnet, from the left hand side of the car, so if you can get someone to move the controls when you look at these, they lower two should move to move the flaps.

If they don't then the usual problem is either they have come undone from the inside, (easy fix) or the the splines have gone (not easy fix :confused:)

View attachment 20012

Inside view from left hand of car.

View attachment 20013
Fantastically helpful photos! Much appreciated.
 
One thing I haven't seen mentioned here yet is that the foam gaskets in the heater degrade and fall apart. I had that on my car and had too much heat in the summer and not enough in the winter. So, if the flaps look like they are moving it could well be that. I dismantled the heater unit and replaced all the old foam with modern sealing strips. Get closed cell foam if possible as it won't retain water and promote rust.
 
One thing I haven't seen mentioned here yet is that the foam gaskets in the heater degrade and fall apart. I had that on my car and had too much heat in the summer and not enough in the winter. So, if the flaps look like they are moving it could well be that. I dismantled the heater unit and replaced all the old foam with modern sealing strips. Get closed cell foam if possible as it won't retain water and promote rust.
Excellent advice, thank you! I won't get to check it out now for a couple of weekends, but will post back when I get to.
 
All valid advice, however a simple fix is to install a tap in the heater hose. Living in Melbourne (which can sometimes get extremely warm in summer, though we can also have summer cold snaps) that solution works.
I recognise it reduces engine cooling due to the removal of a small radiator from the circuit, but seems not to do much to the running temp.

Best tap is a ball cock as used in small bore hydronic central heating.
.IMG_2456.JPGIMG_2457.JPG
 
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Personally I would not put a tap in the heater water pipe as there is a chance that the coolant flow around the cylinder head might be compromised . The cooling system is designed to have a permanent water flow through the heater. I was involved with the engine design engineers when I worked for Rover Group and it was surprising to me how small changes could have a significant negative effect & vice versa. It may not have any affect at all or perhaps only if fully loaded towing a caravan over long mountain passes in the alps, but I would not take the risk.
 
Personally I would not put a tap in the heater water pipe as there is a chance that the coolant flow around the cylinder head might be compromised . The cooling system is designed to have a permanent water flow through the heater. I was involved with the engine design engineers when I worked for Rover Group and it was surprising to me how small changes could have a significant negative effect & vice versa. It may not have any affect at all or perhaps only if fully loaded towing a caravan over long mountain passes in the alps, but I would not take the risk.
If I recall correctly the heater hoses also provide heating and cooling to the intake manifold, I agree with @roverp480 that closing it off isn’t a great idea.
 
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