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Hi, I have been doing a bit of maintenance on the system in a recently purchased property. It has been flushed numerous times for various types of work, from removing existing rads for flushing to fitting new rads, and fixing obvious leaks around the cylinder (all joints PTFE wrapped and compound applied).

I will be having a new unvented system instaled in the next 2/3 years once other works have been completed - until then i want to get the rads and corresponding pipework to a level where it is safe and efficient. As the carpets come up in say 6 months i will be lifting the floor boards and checking the pipework further with a possible view to changing some of the 8mm to 15mm to ensure future reliability (and less chance of blockages). In the interim I have added cleaner after the last lot of works a month ago and am about ready to flush and add 2 bottles of inhibitor to get me through the next 6 months (possibly much longer if i decide not to disturb anymore pipes).

The system is 13 rads with a combination of 8mm and 15mm pipes going to random rads/towel rails. The house is 4 bed with the 20 yr old boiler mounted in the kitchen at the far end of the house, whilst the cylinder, diverter valve and pump is more centrally located on the first floor.

I have refilled the system quite a few times now and after endless tries i can still hear air going through the return pipes into the loft, even now after a month - is this normal that i would be bleeding the system probably once/twice a week? I always start at the bottom working the furthest rad from the pump as opposed to the boiler, i then move upstairs doing the same but attacking the rad above the boiler first as this is the only one that normally needs bleeding and is the first to heat in the circuit (i then do all the 15mm piped rads followed by the 8mm's as all rads are a similar distance from the pump). lastly I release the screw on the pump and let water flow for a few minutes before closing the screw and firing up the central heating circuit until the rads are warm, then the hot water circuit until the water is warm. We don't use the hot water option a lot as we have an electric shower for now and dishwasher - the rads all heat without issues so no blockages and the air from the rad above the boiler doesn't smell eggy so no massive corrosion issues. Since the cleaner went in the rads have been used daily too... there are no leaks on the rads hot or cold (or any other visible parts of the system), i have cleaned the header tank of the brown sludge (which hasn't returned) - my only thoughts are tiny leaks below the floors that i can't yet access (most likely downstairs as no ceiling leaks visible).

Worth also noting that the system hasn't really had more than a month of use before me working on it so this next fill will be the longest time it has gone.

Can anyone offer any help please? :teeth_smile:
 
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could be an old gravity system converted to fully pumped, with f&e feed not at neutral point hence drawing air into system. Or that your regular flushing and bleeding is just not letting things settle and balance out. However if it was mine, i would gut the lot and start anew to get a reliable clean system especially if i intended to stay more than 5 years.
 
Thanks :)

Cost will be the biggest factor as we will be having children in the forseable and redoing the entire system would add a good amount to the bill, I also have a further bathroom/en suite and kitchen to refit - i know it would make god sense but i am limited with what can be done.

I've just asked my plumber to pay a visit to pass his opinion on the matter too for good measure.

The house build was in 1983 so I think the system is the original - the boiler certainly is (making it more than 20 years old ;) ). There's 2x 22mm pipes coming from the header tank both to the same 22mm pipe, this disappears beneath the floorboards at one end and the other routes to the pump, then to the diverter valve where it splits to the heating/water coil.

Does this narrow it down?
 
Sounds like you have a combined feed and vent with pump on the negative side.
If this is correct, then if it was properly done it is supposed to not pull air in or have pumping over problems other systems have. However, I think they can draw air in and I prefer to have a sealed heating system (boiler has to suitable) if the system is sound and no leaks or weeps.
You are best to get a good heating engineer to come in and advise what they would recommend.
If workmanship is poor or any serious previous corrosion, I would prefer it all replaced.
 
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Thanks Best - i think you'd be correct in that description. I too would also much prefer a sealed system, something i had at a previous house via a combi.

One thing I'm confused about is how it would draw air in? the feed pipes obviously feed from the tank into the system and at the same time vent air up through the same pipes which comes up through the header tank base, through the stored water... the water in the header then replaces this new found space does it not?

PS I've noticed running the pump on low helps to get rid of a lot more air generally.
 
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take a look in your attic and it will become clear, trying to explain the how is too much on a sat evening for me. trust me that you are!
 
No worries :D just about to get on it myself

I know what's up there and the ball cock seems absolutely fine. I can't see how it's sucking air in as the inlet outlet pipes are submerged in a foot of water at the bottom of a full tank. Air escapes from the system, surely it's ridiculous for it to be sucked in through a body of water
 
Very correct procedure is how I was taught meaning Vent/ Cold feed / pump. That's the arrangement of a neutral system
 
That's probably the only thing I can do. It may be worth getting my head under the floor boards to check for any signs of leakage.

I asked the question initially as I can't see how a system cannot clear itself of air over a month, when all rads appear to be fully operational - unless the boiler could harbour a few locks?
 
No worries :D just about to get on it myself

I know what's up there and the ball cock seems absolutely fine. I can't see how it's sucking air in as the inlet outlet pipes are submerged in a foot of water at the bottom of a full tank. Air escapes from the system, surely it's ridiculous for it to be sucked in through a body of water

what about the vent pipe pointing into the f&e tank from above, might be time for you to just leave your system well alone for a bit as advised previously!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
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You mean the overflow pipe going outside? I can assure you the vent pipe from the system is at the bottom of the tank and is the very same pipe that feeds water into the system, I've witnessed the bubbles coming up when the system is venting.

I will leave it alone after the next flush as mentioned, I was asking advice on anything else I need to think about regards the trapped air.
 
NO I dont mean the overflow, normally you have an expansion pipe over the tank, re trapped air just stop stuffing too much cabbage
 
You are infact correct :).. This is a 22mm pipe which goes about a foot above the tank. I see what your saying now, guessing there's not a lot I can do to aid the situation when refilling?
 
You mean the overflow pipe going outside? I can assure you the vent pipe from the system is at the bottom of the tank and is the very same pipe that feeds water into the system, I've witnessed the bubbles coming up when the system is venting.

I will leave it alone after the next flush as mentioned, I was asking advice on anything else I need to think about regards the trapped air.

It sounds like your pump is on the return to the boiler? Is the cold feed also on the return and the vent on the flow if it's old skool? You mentioned pipes in the roof so not far below the F&E tank?
Not knowing the exact layout of your system it sounds like the pump is drawing in air, possibly through rad vents or auto air vents if you have them, could well be the pipework in the roof is actually at negative pressure due to the height and the pump position.

I would look at resiting the pump onto the flow after the boiler with the cold feed and vent connected to the flow between the boiler and pump, that way the whole system is then under positive pressure and shouldn't draw air in.
 
Looking at it i think the cold water feed and vent are both before the pump, the FE tank is above the immersion cupboard approx 3 meters up, the only pipes going to this are the 2 you can see in the picture and the overflow. Knowing what i have to work with space wise there wouldn't be an easy way to put the pump before this manifold as the 22mm pipe disappears beneath the floor to a very cramped area - near the boiler is also extremely tight leaving no place for the pump either.... This will obviously all be addressed fully when the unvented and new boiler get fitted at the back of my garage (behind the kitchen wall)
 
You need to get some air vents either side of the 3 port valve in the picture,trapped air has nowhere to go as it is
Your pump is on the flow from the boiler, if after fitting air vents problem still persists,combine the vent and cold feed (tee the vent pipe into the cold feed)
 
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