Central heating problem

[Neil Barker]

My father has a problem with his central heating system and I'm hoping someone might know what's going on. Here's what he's sent me:-

Went on holiday for 2 weeks C.H. left on with t/stat turned down to

15C, H.W. turned off.

On return t/stat turned to 20 C and H.W. turned on. All seemed O.K.

Next a.m. Boiler started up on C.H. switch on and then cut out on temp after only 2 mins. (system cold). Found air in pipes by circ. pump which is on 1st floor. Opened bleed screw and purged air. Boiler re lit itself and all seemed O.K. except for noise of water moving thro. pipes and rads. Subsequently I am daily having to bleed 1 or more of the rads and also use bleed screw by circ. pump.

When bleeding with the circ pump off I get air out but when it stops I don't get water out as you would expect. Have checked header tank and there is water in, though there is no sign of any change in water level as you may expect as a result of fresh water replacing the air.

There is no sign of water leakage from the system.

Suggestions gratefully received.

[Andrew Gabriel]

The level in the header tank should be fairly constant as it will be topped up when you bleed air out. (It will go up a bit when the heating system is hot).

One thing that can happen after some years is that the feed pipe from the header tank can block with limescale, just where the water temperature in it changes from cold to hot, particularly if the system has had a long term slow leak in the past.

[Neil Barker]

The system was drained down about 3yrs ago in order to change the diverter (Y) valve and has worked OK ever since.

What is in the device where the cold water feed enters the cistern with the hot water feed immediately prior to being fed into the circulating pump ? My father is wondering whether this is a possible cause of a blockage ?