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Heater problem

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Hi All,

Took out the 4A today for a lovely run & although I did not really need it, the heater appeared to not be working. On my return I found that the system was almost cold from the connection near the thermostat all along the chrome pipe running along above the spark plugs to the heater hose. The other heater hose was also cold to the valve on the block. That valve was hot as normal.

Obviously there appears to be an airlock or blockage somewhere along the run as described but where shall I look first?

Everything else was as normal. Temperature was where it always is at this time of year & radiator was to the top.

Thanks in advance.


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Hi Monty


I trust you know that at the best of times the heating is spartan and meagre. If the valve was hot it is either hot from convection from the head and engine generally and possibly the valve it not opening. I had the same problem and have it again yesterday but not had time to fix it yet. Try removing the cable ( well losen it) and then with your hand move the valve open and shut many times with the engine running. If that does not open the flow remove the pipe and once it gets going you can reconnect. (careful anti freeze and paint so have a bucket ready and you can always put it back in the rad). I am considering buying a new matrix just to boost the amount of heat. Our problem is we dont drive it with the roof unless monsoon rains suddenly appear. If you look at Rimmers they are selling a new heater and a different valve but I have no idea if they are any better than the standard Smitth unit. The claim is they are.



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Hi Monty, if it is the valve I can recommend the improved valve that Revington sell, it may be available from others, it comes with the hoses and operates very smoothly, it is a little expensive but it works, cheers, Andrew

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Hi Monty,

The heaters can become iffy overtime. probably rust and stuff clogging the matrix.

Uncouple both pipe and flush through in both directions with a hose.

Or fill with rad flush and leave for a while then flush.

Check the flow out of the valve and/or the pipe on the side of the engine - it has been known for the pump impellor vanes to wear away.

When working it should be very good at foot level. Screen demisting is interesting.

If the output of the valve is poor then a new expensive heater will not work as well as it should.


A worrying thought - if the heater matrix is bunged up then the water jacket around #4 cylinder could well be choked also.



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