No flow around cylinder loop

[diyPeterB]

Hello,

I have just moved my cylinder up to the loft and raised the tanks which were in there up above it. The system is a vented, fully pumped, indirect one.

With only the cylinder loop connected to the boiler (no rads hooked up yet) the flow gets very hot right up to the cylinder coil inlet, however the return is practically cold and the water in the cylinder is not heating up.

I have cracked open the cylinder unions and let any air out from filling etc bu to no avail. Given that the pump is simply circulating around the cylinder loop only I am looking for suggestions as to how the heated water gets up to the cylinder then just stops? Even if it was blocked surely the flow pipe up at the cylinder wouldn't get very hot?

Thanks in advance for any help!
Pete

 

[Agile]

Are both pump valves open?

Have you done the bucket test on the pump?

Tony

 

[twgas]

You shouldn't have to crack open unions to remove air, should have fitted bleed points.

 

[diyPeterB]

Ok pump is working fine and valves are open. And I have now fitted means to bleed the air at the cylinder return (which is the highest points save the F&E tank.

Still hot water gets to the cylinder but no further, so this also indicate pump is working but something is preventing flow all the way round..

 

[Agile]

If you have not done the bucket test at the pump then how do you KNOW that it is working and the valves are open?

Hot water getting to the cyl only means that gravity is still present!

Tony

 

[diyPeterB]

Bucket test shows pump is ok and pump valves are open.

 

[gigz]

flow goes to top of coil, is there a vent there ? Undo coil and blow through it make sure there's no blockage.

 

[diyPeterB]

Ah, I have flow on bottom of cylinder

Will switch them round this afternoon, see if that helps.. I have blown through the cylinder when dry and it was clear.

Pete

 

[diyPeterB]

Also I have a manual valve to bleed air from next to the cylinder - is an automatic vent valve required if the cylinder is the high point on the heating circuit?

 

[matt1e]

whats the boiler doing?
is it cycling or cutting out on over heat
I think t may be helpful if you posted a sketch or some pics of the layout

Matt

 

[twgas]

Seen hundreds of fully pumped systems with flow at bottom, it shouldn't be the cause of your problem.
As said, pics might help.

 

[Agile]

On a pumped system the flow can be connected either way round!

Tony

 

[diyPeterB]

Thanks for the replies, we now have water pumping around the system. To do this I connected a mains supply by the cylinder and back-filled the system, then once started up I bled a lot of air out of the pump (previously had been some air in pump but bleeding did not help).

There does sound like some air still being pumped around - I am thinking of putting something like this air separator in to help resolve this and reduce the noise - would this be advisable?

http://www.toolstation.com/shop/Plumbing/Valves/Air+Separator+34/d20/sd2696/p97455

In trying to understand why the system won't just fill and run the only theory I have is that some horizontal pipe runs aren't actually horizontal and do dip down and back up - could this create air locks which prevent water getting all the way around? If so I will have to flatten them out so the system fill as expected..