Overheating boiler / pump

[JB277]

I\\\'ve had several problems with my central heating / hot water system since switching the CH back on when the cold weather started this year, most of which I\\\'ve solved but I\\\'m now stuck and would like some help...

To cut a long story short, I\\\'ve successfully replaced the programmer (from an old Randall dial one to a new electronic one) and replaced both the HW and CH two port motorised zone valves. After everything was complete and working properly (valves opening as called by programmer / thermostat, pump starting and boiler firing up as called for, radiators warming up etc), I bled all the valves on all the radiators - most of them had very little air in them apart from one of the upstairs radiators that took about 45 mins to bleed out. After completing this last radiator (everything was fine before this), the boiler then started to overheat and cut out very quickly (15 secs rather than the few minutes as normal) and on doing this the flow pipe coming out of it would distort along its length, make hammering and gurgling noises, and sound like something was being dragged through it on the inside. Additionally, the pump (Grundfos 15/50) heats up very quickly (very hot to the touch) and also appears to fail to switch off when it should.

I can\\\'t seem to get it working again, but I think something is either blocking the pipe out from the boiler somewhere along its length, or that bleeding ALL the air out from the upstairs radiator has caused a blockage somehow (the pipe that seems to be making the noise appears to go upstairs to the radiator, rather than to the pump / HW tank although this doesn\\\'t make sense to me..).

I\\\'d be very grateful for any help on this matter what with winter on its way! Cheers.

 

[pf_mills]

The fact that the radiator took sometime to vent indicates that either the make up supply,from F&E Tank is restricted and/or there is debris in the pipework supply to the radiator.

Frequently the 'T' where the make up enters the system gets restricted/blocked.

Either way to me it indicates that the system may be sludged up and requires cleaning. Powerflush is the answer, however draining and re-filling together with a restorer..read the instructions.. may help considerably. Maybe it is too late for your pump!
You could try gently tapping the make up 'T' in the hope that it will dislodge something.

Hopefully you will get a second opinion on this site.

 

[JB277]

Cheers for that. I think the pump is working actually. Also, you were right, the pipe making the noise does indeed go up to the F&E tank. Another quick question: how full should the F&E tank be? I had a look last night and it's almost empty - would filling it up a bit help at all?

 

[pf_mills]

Well it wants to be above the outlet. Outlet could be at bottom or the side.
The float v/v should control the level..is it stuck? Half way up should be ok. I like it quite full but I have seen comments that thist may be too high..it ha sto accomodate the expansion due to increase in water temp.. quite often the tank will empty (evaporate) during the summer if the float valve sticks up.

 

[JB277]

Just to let you know, it's all working now - the F&E tank float valve was indeed jammed and also we managed to unblock the pipe from the boiler into the tank by blowing down a length of hose into the pipe which dislodged whatever was in the way. We know have a fully functioning central heating system! Cheers for your help pf.