Worcester Bosch 28i series 2 not heating radiators

[D G Hart]

Hi, I have a microbore heating system with the above boiler, now 18 years old. recently, I had 3 radiators replaced and all worked fine for about 3 weeks. Now however most of radiators are only getting warm, some hardly at all. The pump is running and the whole system has been bled and topped up with filling loop. Burner will only stay on for about 40 seconds then cut off accompanied with gurgling noises. As a layman, I think the pump motor, although working ok (checked it's free) is not driving the impeller as it should and circulating the water correctly.
Questions. 1 does this sound like a correct diagnosis? and 2 if so, should I have the pump replaced or the entire boiler,
Thanks in advance, all opinions gratefully received.

 

[ShaunCorbs]

Air lock

 

[D G Hart]

Air lock

How can this be got rid of? have bled all radiators. is there a bleed point on the pump or heat exchanger?

 

[ShaunCorbs]

Where's the filling loop on the boiler ?

 

[D G Hart]

Where's the filling loop on the boiler ?

Hi, it's directly below the pump. After 3 weeks good operation 2 things happened. Rad closest to boiler suddenly needed bleeding (System refilled) and there was a grinding noise for about 30 seconds which I THINK came from the boiler. After that, I noticed some rads no longer getting hot

 

[ShaunCorbs]

Turn all but the closest to the boiler off and turn the heating on you might have to bleed that rad a few times

 

[Rob Foster]

op does not mention filter, sludge, chemicals regular maintenance.....18 year old system ...its done well
centralheatking

 

[D G Hart]

Turn all but the closest to the boiler off and turn the heating on you might have to bleed that rad a few times

Hi and thanks for the advice. Did as you asked but although burner came on and pump sounds/feels to be running (bit noisier than normal?) the pipes to the rad remained cold.
As layman, suspect pump motor shaft and impeller no longer connected. Your thoughts?

 

[kris]

Hi there, defo sounds like a pump circulation problem , the boilers cutting off quick as water not moving fast enough so overheats , although not sure if pump is inside or outside boiler or what kind of system you have,

 

[D G Hart]

Hi again and thanks for your time with this issue. I have now had a plumber come and check the system. He replaced the pump giving a small improvement but feel the problem is a partially blocked heat exchanger and as such, has recomended an Ideal Logic 30 boiler and a powerfully of the system. It would seem the recent radiator change has disturbed a lot of sludge and caused this problem. Thanks again for your time and knowledge. Cheers