Heating not happening

Golf mk4 2001 X-reg
1.6 8v AVU engine Automatic

This is a long post so bear with me....

Started from cold, and drove about 4 miles into town. Varying road conditions (uphill down hill, and a couple of quick straights) and also having to stop at two sets of traffic lights..

Now engine temperature rose to operating (90 degrees C) pretty much as normal, but the interior heater remained cold,

Now i'm familiar with car cooling systems, and usually the sign of a failing heater is low coolant, so i stopped and checked the levels which were fine, Down, but nothing to make alarm bells ring. The bottom hose from the Rad' was cold also, so i suspected thermostat or Rad..

My gf's dad came out and had a look and he's been in the motor trade for decades, we left it idle for about 20 mins / half hour keeping a careful eye on it.
The top hose got pretty hot, as did various other hoses as expected, slowly but surely the heater got warmer and the cooling fan behind the rad cut in after a while....fine.

we put it down to a bitterly cold night (which it had been) and that it simply took longer to get warm than expected....

I left Aberaeron this afternoon to go to my 2nd job, and on a 15 / 20 mile journey back to 'Lampeter' the heater yet again failed to get warm.

I've checked the radiator to make sure it's not blocked, it's fine as i can practically breathe through it (althought i dont fancy this haha)

Having a lot of difficulty getting to the pipes for the heater matrix to check if thats simply blocked or not

How is the heater temperature control dial operated?
i.e on a mk4 fiesta it's electrical contacts controlling a valve on the heater pipes which is prone to failing and remaining stuck on one setting, hot or cold usually.

With the golf i can operate the dial and it feels normal, and i can hear what i think is a flap moving inside the dash, channeling the air over the heater matrix or not. If i turn the control to fully cold, make a mental note of the temperature of the air on my hand, then flick it to Hot, there is a marginal difference, still cold, but with out the edge, as if it is circulating air from the cabin...

i've now got it back together and filled the system, but now it's boiling up inside

Vag-com reckoned engine temperature of about 115 degrees, but the instruments read 90, as if it is physically unable to go past 90...

Car's now parked up in the corner of the yard, highly p*s*ed off with it.


I've shortlisted possible solutions:
1) thermostat
2) air lock
3) Water pump
4) Blockage somewhere
5) if there's any truth with the valve on the heater pipes, that being the cause...

I'm gonna re-drain the system in the morning, and re-fill it again and go from there....

Any help and advice is appreciated

what a pain m8, what about running a hose into the water bottle while the cars running and undo the bottom hose to see if its running thru the system okay, just a thought am no mechanic

hope u find he problem m8

turned out to be water pump.

Common fault, plastic impeller breaks off the spindle so it just sits there idle and useless.
Was a good oppertunity to fit new cambelt and tensioner too

Sorry only now seeing this, Same issue we had on a A3 this week, turned out to be the water pump.

what wud u know ^ lol

should see my new toy kicks cupras ass, suzuki sj 413 jeep all jacked up with massive mud tyres, amazing fun been up and down every hill/mud bank in miles

6 of us have bought off roaders stu get one its better than any car! il post pics up from todays outing in a bit

glad to hear you got it sorted