heater not getting hot can anyone help please

[monkey]

my heater only gets warm . i have flushed the cooling system and replaced the thermostat . i ran a hose pipe though the heater matrix to see if it was blocked but the water ran though fine . any ideas welcome as its going to be a real pain clearing the screen on winter mornings .

[chris_325i]

Have you checked the new thermostat is working properly, as a thermostat thats stuck open will increase the warm up time alot.

also make sure all the air is bled from the system, whats the temp gauge go up to ?

Chris W

[aj_mckay]

Air lock? check system bled correctly...

[eko]

Knackered heater valve?

[leeparkes]

what engine is it?

[monkey]

i did think of a knackered heater valve eko how do you know for sure as it is letitng some hot water though . dont think its an air lock as i have an old rad cap with a piece of pipe on it with a 2l can on the other end of the pipe i hang the can from the open bonnet so there is water pressure to push out the air from the system . and lee its an m42 .

[chief]

air block or not enough water is the favourite

where on the temp dial does it go to when on a 5+ mile journey

also put your hand on the pipes that go to the heater

that will tell you something too

HTH

[monkey]

the temp gauge sits in the middle of the range . i think the pipe going in to the heater is a bit hotter than the one that comes out . i guess i have the pipes the right way around the one from the back of the head goes in to the heater and the flow out of the heater goes to the bottom of the rad

[chief]

that seems good to me
do you have a bleed screw above the thermostat housing
have a play with that to get some air out
after that my knowledge has been exhausted
good luck

[daimlerman]

Pipe from the back of the head should go to the lower heater stub.

[monkey]

thanks and it looks like my pipes are right then . will have another go it tomorrow

[Ilkorin]

I hear that the best way of getting air out of the heater system is to undo the upper hose to the heater and pull it out slightly with the engine runnning to push all the air and a little water out then clamp it back down... then it should be all clear.....

from that point it might be worth checking the valve is ok and the heater matrix isn't blocked by trying to flush water through the heater matrix (I believe it's bottom to top but if someone could confirm this - it's important not to flush it the wrong way)... the valve defaults to open when the engine is off so it should be free flowing

hope that helps some, I'm sure brianmoooore will be on it soon and all will be well :p

[Brianmoooore]

In my experience, if a heater consistently gives ANY heat, then it is not airlocked, but in your position, I'd still give it a try.
Partly blocked matrix or electric valve must be the main suspects, but there is still the possibility of a mechanical fault of some kind with the air blending flap or the cable to it.

[monkey]

i have just looked at where the hot/cold cable goes to the air flap and it looks to be working but i cant see inside the heater box to see if the flap inside is moving . i have run water though the heater both ways so i guess it cant be the heater valve as that would stop the water running though the matrix wouldnt it ? i did think that i may need to look at the pipe on the back of the cylinderhead to see if it has got rusty and partly blocked as i have had one of these pipes rot away and leak on my other m42 .