water circulation prob

[stuart01]

hi
have 1998 a4 with .9 tdi eng code afn heater started to blow cold air
checked thermostat and waterpump no visible defecs but replaced both
fault remains further inspection reveals water not pumping to heater matrix
if i remove thermostat water then pumps to matrix have checked for blockages all clear
this would point to water pump but then it pumps well with stat removed ?

[phil miller]

if you have replaced the stat and its the same then the water pump is a good place, you say you have checked it, was the pump hot when you checked it? reason i ask is years ago had a similar problem, took the pump off impellor seemed fine, but when it got hot thats when the impellor went free, when cold it was solid, do you lose any water?

[stuart01]

i removed and replaced waterpump with pump that has brass impellor

[mumutley]

Hi
Did you replace the thermostat? if not, its time to replace it with a new one (it may work in a bowl of boiling water but not on the car)

Is the water pipe hot up to the bulkhead? and the return pipe cold?
If this is the case the heater matrix is blocked
Remove both pipes, feed garden hose in to return side of heater matrix and blast it through (this will be reverse of normal flow)
Then do it the other way
Refit hoses and fill coolant system and retry