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Discuss Air in heating g system - Already had two plumbers fail to diagnose. in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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The air is being sucked in via the vent so if you seal it the air wouldn’t get in also you would run it at a pressure of 1 bar not 6

you’ve said you had it pressure tested for leaks so in theory the system would be ok sealed

try turning the pump speed down to 2 it’s on 3 atm
The guy pressure tested it at 2 bar. He said he didn't want to go any higher just in case.

I already turned the pump down to 2 and it made no difference. I turned it up to 3 hoping it would address the cold radiator issue I mentioned in my original post. It didn't.
 
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Thanks for the replies. Here are some photos of the unvented tank and components around it. I have also attached a vid up in the loft showing the feed and vent pipes and a few photos. At the end of the video, the pipes drop down to the airing cupboard (hot water tank).

I considered sealing the heating system when we replaced the vented tank, but it was spending money on something that to my knowledge at the time provided no additional benefits. The heat-only boiler was replaced before we considered the extension, so we never considered an alternative (the old one died on us so we just needed a new one asap). We also have very high water pressure coming into the house (6 bar which I assume you’d have to limit) which is great for showers but scares me a little connected to a 25-year-old heating system. If I was to replace the open system with a sealed system am I not just masking the underlying problem? Would the air currently going into the F&E tank instead just trigger the pressure release valve?

John.g – you said it looks like there’s been something wrong for a long time based on the condition of f&e. Can you elaborate a little? There’s a thin layer of sludge at the bottom but other than that it looks ok to me.

Thanks again.
There should be no sludge of any description in that tank.
I had a look at your attachments but you can inform easier on your set up, Is the pump on the flow from the boiler and if so the accepted way of installing the vent and feed is (from the boiler) vent, cold feed then pump with the vent and cold feed no more than 150MM apart, if not like this you might show where the cold feed tees into the system.
Another way and better IMO is to have a combined vent and cold feed like my > 40 year old system which is spotless.
You can convert to a sealed system obviously or convert to the combined vent & cold feed which only needs a few litres of water drained down and almost guaranteed success, just ensure the vent is clear, the insulation looks kinked on it but I presume the actual vent isn't.
 

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Could be, and if so then points to some blockage somewhere but far better to combine high up like mine as the cold feed "can't" have a blockage and as long as the vent is absolutely clear cannot vent or pump back.
 
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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.
 

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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)
 

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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.
 

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