All radiators cold after draining system.

[ns3270]

6 weeks ago I put Sentinel sludge buster in the radiator system.
Today I drained the system, refilled it, bled all the radiators, switched on but no radiators get even mildly warm. The pump and pipes either side it are very hot. The input pipes to the first couple of radiators are quite hot.
I replaced the pump 6 months ago - it's a Grundfos Super Selectric 15-60-130.
I've removed the big centre screw from the pump and it drips very hot water, isn't this supposed to cure an airlock in the pump?
Any ideas what I should try next?

 

[gas4you]

On the face of it, it sounds like a serious, but basic air lock.

It would help if you told us what type of system you have. eg, combi, open vent, HW cylinder, sealed system etc etc

 

[ns3270]

It's not a combi or sealed system - I guess it's just a regular hot water cylinder system.

 

[kevplumb]

mabye a daft question but is the pump running

 

[ns3270]

It was certainly running fine this morning before I started draining. It's only 6 months old too so it should be OK. It's still hot but I turned it off an hour ago. I took the big screw out and a little water came out. I then moved the control from 1 to 2 to 3 and the noise level increased which suggests the pump is OK.
How else do I test whether it is working?

 

[gas4you]

Check pump as Kev suggests, then if working turn off HW and just put CH on, close any bypass valve, set pump on max speed and turn off every rad except the closest to the pump.

See if this will push the air lock out.

 

[ns3270]

I've closed all the radiators except the first, switched on, and the first radiator is now really hot (it got hot at the top first which seems odd).
What do I do now - try the second one etc?

 

[gas4you]

Yes, just go round each on until they all get hot, then leave them all on.

They will get hot at the top first because hot water is lighter than cold so rises to the top of the rad first, hence why you are best to bleed rads when cold

 

[kevplumb]

yup

 

[ns3270]

Many thanks for your help - the first 3 are hot now so on to the rest.
Will the air lock appear at the top of one of the radiators which I can then bleed?