Dreaded air in upstairs radiators and heating is off

[Johntheo5]

A little more detail on previous boiler did have air ingress on that system and that's why the H was modified and that did not have any effect so my hesitancy on changing to combined vent and feed. Eventually on the previous boiler managed to remedy air ingress by balancing the radiators. Could that have been by chance?

I don't don't how balancing the rads would have any effect.

Coming back to present arrangement it is very noticeable the suction on start up on the feed pipe for 20 secs and on the vent pipe for 1 or 2 secs.

Yes, I don't know if thats normal or not or due to some restriction in the H, it doesn't take much to cause that.

The orifice that is connected to the feed pipe is 10mm diameter at most so why is 22 mm pipe required.

Yes, probably OK with the 15mm pipe, my tank does have a 22mm tank nozzle.

Just a thought on the air in more radiators now. Could that be because I am circulating cold water and not hot.

Number of rads shouldn't have any effect IMO. I would recommend circulating at a high boiler temp like say 70C and then switch off boiler/circ pump and then vent.

Still surprising the difficulty in filling normally, is the system zoned?, if so, the zone valves should be latched open before refilling and all TRVs, if installed should be fully open.

All thats changed so is that you have installed a new boiler, most of these boilers have a internal automatic air vent but this is generally shut off after venting, you may not have access to this as you can't remove the boiler casing, so maybe just go ahead and modify the system to combined vent and cold feed, let the feed pipe connected at the bottom as suggested and install a lever valve for venting, at the top. I would also install a lever isolating valve/gate valve on the 15mm mains supply to the F&E tank ballcock to facilitate controlled/very slow refilling.

Where did the original cold feed go to before modification?.

 

[nairb999]

Thankyou for detailed response John. The original cold feed was directly above the pump on the horizontal flow pipe. I was advised on this site to move vent and feed closer together.

This morning with the help of my wife I have performed a number of tests. With the pump circulating I held my finger over feed until suction stopped and this created a little more noise in pipes. Turned the pump off and trickling water noise in pipe work. I then placed palm of my hand under vent pipe and started pump. No noise on start up. Left it for a few minutes no apparent difference in pressure when removed my hand plus no noise at all in pipe work. I have now started the pump again with my hand under the vent. After a min removed my hand and will test again after a few hours to check progress

 

[Johntheo5]

The test you did won't tell alot because the pump must always have a leg full of water or a expansion vessel above it, when you blank off the cold feed with your hand the pump will draw down that leg of water in the vent pipe very rapidly because there is still air in your system and is compressed a little when the pump starts.( or something like that)

Why don't you tape a fairly strong plastic bag, like the ones you get at airport departures, around the vent, if too much pressure builds up for any reason then the bag will rupture at a very low pressure, you need a few days running like this to get rid of all the air.
I would just do the mod, you have nothing to lose.

 

[nairb999]

Thanks John. Will give the plastic bag a go first. This my feed and vent just before going into the loft. So I can disconnect 15 mm elbow and t into 22 mm vent? Then cap disconnected feed pipe here and connect lever isolating valve/gate valve.

ps never got round to filling ceiling gaps properly

 

[Johntheo5]

Yes, Give that a go.

 

[nairb999]

Plastic bag in place and will run for a few days. Just one question now if I end up with combined vent and feed solution I will install a valve as suggested. Do I leave the other side open or make a blank

 

[Johntheo5]

Not sure what you mean by the other side, if you want to leave a section of the cold feed in place incase you want to revert to your original then you you cut it close to where you are Ting it into the vent, that only leaves one end open, this is where you install the valve as this leg will fill with water and the valve can be opened to vent the air out of it and closed when water comes out.
If you do a permanent mod then cut the cold feed say 80 to 100mm or so above the main flow pipe and just install a compression coupling with its end capped off.

 

[nairb999]

Sorry John but Looked for a valve that could be suitable. So original feed pipe goes into one side. What do I do with the other side?

 

[Johntheo5]

This is what I mean.

 

[nairb999]

Thanks for clarification John so the other side I just leave open. I am an electrical engineer haha

 

[Johntheo5]

Don't forget to increase the F&E tank level by bending the ballcock arm.

 

[nairb999]

Yep. This has been actioned