No flow through rads - Help!

[Knappers]

Bad day today, please help!
I've been to a job on a vented heating system with no heat (poor flow) in downstairs rads, well all over really.
I bled a little air from manual vent, checked the 3-port was motoring, roughly balanced lockshields and checked pump was spinning.
no luck

I isolated all but one rad and still no/very little flow in some areas.
Removed pump and checked/cleaned veins on impeller and checked F&E tank.
no luck

I tried flushing flow and return through individual rads (with and without vent capped)
no luck

I can flush to hot both ways water is clean and flow open ended is reasonable (10mm) but when I reconnect and run theres no flow.

Ive shut bypass and can feel heat traveling up pipes at a reasonable rate but must be poor flow due to blockage (air or debury)

Cant think what else to do short of stripping off 3-port to check ports free and temporarily 'pressurising' system to flush with mains pressure.

Am I missing a trick?

 

[Best]

Turn all rad valves off (both sides of each rad) and remove one rad that wasn't working. Open each valve for that rad into a hose. If each valve keeps flowing, then no blockage is there. Rads must be dirty or pump is not working properly.

 

[joni os]

Temporary replace pump with one you know to be working, make sure all air vents are working, including any that might hidden in airing cupboard etc, and make sure system is not sucking air.

 

[jtsplumbing]

First call replace Pump !

 

[Best]

I agree with always considering the pump. The odd head scratcher I have came across where only a few rads were working, or none at all, turned out to be due to a faulty pump which often was nice and clean inside it and appeared to be pumping fully.

 

[Unregistered]

Thanks,
I recon its most likely air locks.
strong grundfos pump with genuinely clean impeller cant see it being that.

If I cant clear the air by flushing individual rads what do you think is the best way to clear?

 

[PlumbBobBob]

how have you proved the pump is working correctly? oh and put a tick in the remember me box when you log back in.

 

[Knappers]

spins and took head off and cleaned veins and body.
Made sure it was clear and could see right through each one (as I've had a job before that a colleague had checked and said was ok as it looked ok but was actually blocked deep in the veins).
I also had to replace the union valves so they're ok.

 

[Best]

spins and took head off and cleaned veins and body.
Made sure it was clear and could see right through each one (as I've had a job before that a colleague had checked and said was ok as it looked ok but was actually blocked deep in the veins).
I also had to replace the union valves so they're ok.

Maybe the pump is okay, but never rule it out. I have seen pumps that are only a few years old that appear to be working and spotless inside, but some rads - especially furthest rads and any on drops not working. New pump and all working

 

[Knappers]

Ok, worth looking at pump.
lets say air needs a bit more of a push than gravity will allow remembering I've got 22mm to 8mm on rads, what's the best way to push it out?

Was thinking cold main to open vent and isolate feed then flush rads both ways?

 

[macackau]

I went to a call out due to no heating and hot water and the pump looked out of the box brand new. Could feel flow pipe just past pump was cold even though boiler was in and only a few feet away. Was debating if it could be the pump or not. 5 mins to change pump and sure enough all working ok again. Customer a bit upset as pump was a year old. It was a Wilo one, I swapped it for a Grundfos.

 

[AllyBongo]

Any compression fittings around the boiler and pump area? Check for blockages, build up of sludge

 

[joni os]

Similar to above, but blockage in combined F&E leading to air in pump and was cause of failure.

 

[Knappers]

Customer has the arse that I've charged for 4hrs and not fixed it, so not going back - Oh well.
Good luck!

Need a spare pump on the van I guess.