my heater is working great now.....it took the 2 guys 20 mins to take the heater out of my cabinet and fit the new glow pin.......coiled hose temperature after heater running for 20-30 mins was 62c.....they had indeed fitted a brand new glow pin that was a dud!
....just one of them things.....
i got talking to both of them and they said its the worst burner theyd ever seen...they reckon that the kink in the hose(leading to the heat exchanger) had stopped the burner from burning off the soot and that the kink was probably there since installation but had got worse over time and restricted the water flow resulting in less heat......
they said these burner units should last anywhere between 7-10 years so ill hold my hands up i was wrong lads!
anyway glad ive got it sorted now.....just waiting for the gasman to get my heating back on in my flat now as its ruddy freezing!!