Air in heating g system - Already had two plumbers fail to diagnose.

[ShaunCorbs]

If you turn let’s say 5 off does that one heat up ?

 

[John.g]

Getting a bit over my head now but I think it is combined if this (attached photo) is what you mean. The tank has never moved and we never had any problem prior to the installation of new radiators and replacement of the vented cylinder.

A blockage has been mentioned a few times. Which part of the system is likely to have the blockage? Could it be related to the lukewarm radiator (one of the new ones on ground floor) I mentioned in the original post? All other radiators work absolutely fine now I've added the automatic air release valves even with the pump on the medium settings so the hot water is moving about.

Thanks again.

It certainly looks like that (circled) the cold feed is clear I would think judging by the bubbling, can you just blow down the vent and see does it bubble up in the tank.
Where is the vent teed into your system?.

Just ensure it hasn't been changed and taken off close to some motorized valve or on the wrong side of it.
There also seems to be another pipe directly across from that cold feed on the other side of the tank?? (See video)

 

[Quinla01]

If you turn let’s say 5 off does that one heat up ?

No. If I turn all the radiators off in the house and have the pump on 3 it doesn't heat up any more than having them all on. There is some heat getting to it but I'd say on a scale of 1-10 it's 3. It's in the kitchen and luckily I over specced how many radiators we have in there so we have two radiators that do work that just about keep the room warm. See (crude) drawing below. The radiator that's not heating is at the end of the run and feeds back to another new radiator that does work. That then feeds upstairs to a towel radiator which also works. The towel radiator was the first new radiator they connected so it links into the existing system somehow but I'm not sure where. One other data point, during decoration someone put a screw through one of the pipes about 1m away from the problematic radiator. We had a bathroom fitter on-site at the time who quickly bunged the tank, cut at the point of screw entry, and then somehow joined the two pipes. Not sure if maybe that has somehow caused a blockage. If so I suspect it's on the return since when I've released the bleed valve on the problematic radiator and opened the TRV there's no shortage of pressure spraying water out and also the feed pipe gets a lot warmer than the return end.

 

[ShaunCorbs]

Any chance of a pic of the problem rad and pipework ?

 

[Quinla01]

It certainly looks like that (circled) the cold feed is clear I would think judging by the bubbling, can you just blow down the vent and see does it bubble up in the tank.
Where is the vent teed into your system?.

Just ensure it hasn't been changed and taken off close to some motorized valve or on the wrong side of it.
There also seems to be another pipe directly across from that cold feed on the other side of the tank?? (See video)

I'm pretty sure it's the one I've marked below. Not sure if it's expected but where the pipe joins the system very warm and gets gradually cooler to the point of being room temperature towards the ceiling where it goes into the loft.

 

[Quinla01]

Any chance of a pic of the problem rad and pipework ?

Sure but I'm not sure there's much to see.

 

[ShaunCorbs]

Ok try this tomorrow close every single radiator via the trvs if they don’t have a trv close a lockshield valve and turn the boiler temp down and turn on the heating let it run for half and hour or so then bleed the radiator

 

[John.g]

I'm pretty sure it's the one I've marked below. Not sure if it's expected but where the pipe joins the system very warm and gets gradually cooler to the point of being room temperature towards the ceiling where it goes into the loft.

Doesn't seem to be any mods to the vent and pump attachment., the vent is a continuation of the boiler flow pipe so will be quite hot for a portion as this is where the expansion takes place.
I would ensure that the vent is clear right up to where its bent over the F&E tank, maybe just blow down it (boiler off) or stick a hose in it and overflow the F&E tank for a few minutes.

Did you look at the F&E tank again and try and see if there is another pipe opposite to the cold feed at the other side of the tank bottom? or maybe its a electrical wire.

One other thing

 

[Quinla01]

Ok try this tomorrow close every single radiator via the trvs if they don’t have a trv close a lockshield valve and turn the boiler temp down and turn on the heating let it run for half and hour or so then bleed the radiator

Will do. Whats the logic there? Thanks

 

[John.g]

Ok try this tomorrow close every single radiator via the trvs if they don’t have a trv close a lockshield valve and turn the boiler temp down and turn on the heating let it run for half and hour or so then bleed the radiator

Systems with a combined feed and vent can be difficult to fill after a complete drain down, I have a gate valve on my cold feed and just barely crack it open to fill the system on the very rare occasions that I do a full drain down but never have any real problems with air in the system when I do this.