is this feed and vent setup weird?

[andyr123]

trying to get rid of an air lock in our boiler after emptying central heating system and looked in the airing cupboard at this setup . the alarming thing I found was going up into loft at the F&E tank expecting to see the cold feed being a 22mm ... but its only (equivalent) of 15mm - I say equivalent because our house we are in (Ireland) has not got the normal 15mm and 22mm copper piping for the plumbing it has this (expensive) German made metal pipe you can bend easily by hand (more easier than copper) and is covered with some white plastic outer material. The bores look even smaller than 15mm copper does , but its not microbore pipe.

but I think its a weird setup , 15mm (or equivalent) for the cold feed from the header tank in the loft but the expansion pipe 22mm (or equivalent).

here is a rough drawing:

 

[andyr123]

any consequences whilst I have the water drained down to change it to this:

 

[Johntheo5]

I can't figure your system out, but mine, from new, 53 years ago, with some rads over 40 years old has the circ pump in the boiler house, pumping into the (oil fired) boiler (return) the boiler flow then feeds all the rads and the HW cylinder coil, the 3/4" vent is carried on up from the T into the cylinder coil (top, inlet) and up and over the F&E cistern, the cold feed is teed into it as shown, the F&E cistern is spotless.
If you have a external circ pump (on the flow) then the vent must be taken off before the pump suction and can be plumbed up like mine. The more normal arrangement (with pump on the flow) is to have the Vent, then (no more than 150mm away) the cold feed, then the pump.

 

[andyr123]

our central heating pump is on the return in our system in the outdoor boiler unit (so it must be pushing the water in the flow direction rather than pull from the flow.

the cold feed from the loft header tank seems to go on the flow pipe from the boiler rather than the return pipe.

here is a rough sketch. I think this is how I think ours work:

 

[Razor900]

Assuming the 15mn pipe isnt blocked the setup is ok if not textbook.

You have MLCP pipe. Plastic with an aluminium barrier layer

 

[Johntheo5]

our central heating pump is on the return in our system in the outdoor boiler unit (so it must be pushing the water in the flow direction rather than pull from the flow.

the cold feed from the loft header tank seems to go on the flow pipe from the boiler rather than the return pipe.

here is a rough sketch. I think this is how I think ours work:

View attachment 388740

As suggested above, your system should be OK, if no pump over and F&E cistern clean then why change it?, but you could, to make it quite similar to mine.
I have a isolating gate valve on the cold make up to the F&E cistern ballcock and on refilling the system I just crack this open to fill the system very slowly to allow air to pass up through the same pipe that the water is feeding down through. I also have a 3bar PRV right on the top of the 20 year old Firebird Boiler and sometimes vent some air via this, some don't recommend this in case the PRV leaks but mine, the original, never has.

 

[andyr123]

As suggested above, your system should be OK, if no pump over and F&E cistern clean then why change it?, but you could, to make it quite similar to mine.
I have a isolating gate valve on the cold make up to the F&E cistern ballcock and on refilling the system I just crack this open to fill the system very slowly to allow air to pass up through the same pipe that the water is feeding down through. I also have a 3bar PRV right on the top of the 20 year old Firebird Boiler and sometimes vent some air via this, some don't recommend this in case the PRV leaks but mine, the original, never has.

thanks yes I have a 3bar PRV on our outside boiler on the flow. was going to fit an AAV for the same reason there because I use the PRV to vent it but I didnt do it there instead whilst the system was drained I fit the AAV in place of the radiator bleed valve on the flow pipe in the immersion heater airing cupboard .

 

[andyr123]

Assuming the 15mn pipe isnt blocked the setup is ok if not textbook.

You have MLCP pipe. Plastic with an aluminium barrier layer

has 15mm pipe got more chance of blocking up than 22mm feed from header tank do you think . and the 15mm feed there is OK going into the flow of the boiler in the airing cupboard? - when I have looked at setups in my other houses we have lived in I am pretty sure the feed from the header tank went on the return side of things not the flow side.

 

[andyr123]

could i change the feed to this setup so the feed is on the return pipe to the boiler? - would that work? - if so could i keep the feed as 15mm or do i need a 3/4 (22mm) feed pipe there?

 

[Johntheo5]

I would suggest just doing it like in your post #2, if possible tee in a piece of 22mm pipe (cold feed) from the cistern into the vent, doing it in the way directly above (post #9) stands the risk of getting pump over from the vent. its quite likely that there is a blockage, or partial blockage where the cold feed is presently teed in, so best to remove that altogether and just blank it.
I don't like these so called AAVs, they either get blocked up or leak water, should be called AWVs, automatic water vents, I would fit those thumb vent type that you just open and close manually, once you have modified the system and get rid of the air after a drain down, you shouldn't have to do any more venting. I think its best practice to have a 3bar PRV on the boiler despite having a open vented system, you could mount a vent + the PRV on a T piece directly off the boiler.

 

[andyr123]

I would suggest just doing it like in your post #2, if possible tee in a piece of 22mm pipe (cold feed) from the cistern into the vent, doing it in the way directly above (post #9) stands the risk of getting pump over from the vent. its quite likely that there is a blockage, or partial blockage where the cold feed is presently teed in, so best to remove that altogether and just blank it.
I don't like these so called AAVs, they either get blocked up or leak water, should be called AWVs, automatic water vents, I would fit those thumb vent type that you just open and close manually, once you have modified the system and get rid of the air after a drain down, you shouldn't have to do any more venting. I think its best practice to have a 3bar PRV on the boiler despite having a open vented system, you could mount a vent + the PRV on a T piece directly off the boiler.

Thank you for your replies and help. so just to confirm no problem with having the F&E cold water feed from the header tank going into the flow pipe of the boiler then? , it does not have to go/make more sense to have the feed going into the return of the boiler then no?

 

[Johntheo5]

No problem having a combined vent and cold feed with a boiler that has a high limit stat as well as the control stat, but not with a solid fuel boiler.

 

[Johntheo5]

"trying to get rid of an air lock in our boiler after emptying central heating system", just looking at this again, how do you know its air locked?, have you opened the 3bar PRV on top of the boiler, if the boiler/system has refilled after a drain down then there is no blockage in the cold water filling line, is the boiler firing up and not tripping out on its high limit stat? is the system generally clean, including the F&E cistern?, if the boiler is tripping on the hi limit stat check that the pump is running and/or even remove it (if system dirty) and inspect pump ports for blockages, with pump removed, open one pump isolating valve to check for water, then shut it and check the other. I would do these checks before making any mods.

 

[andyr123]

"trying to get rid of an air lock in our boiler after emptying central heating system", just looking at this again, how do you know its air locked?, have you opened the 3bar PRV on top of the boiler, if the boiler/system has refilled after a drain down then there is no blockage in the cold water filling line, is the boiler firing up and not tripping out on its high limit stat? is the system generally clean, including the F&E cistern?, if the boiler is tripping on the hi limit stat check that the pump is running and/or even remove it (if system dirty) and inspect pump ports for blockages, with pump removed, open one pump isolating valve to check for water, then shut it and check the other. I would do these checks before making any mods.

Thanks - you are right , could more than likely be sludge. the water was pretty black and disgusting (but its bound to be years in boiler I suppose) header tank is clean apart from the usual brown sediment at bottom. not too bad though.
when i open 3bar PRV no water flows out as usual , just a lot of hissing air and then stop. nothing coming out of drain tap at bottom of boiler (just a hiss of air then stops, no water now) when I was draining system terrible slow flow out of drain tap, not its usual gush that it used to do with water coming out of drain tap and PRV (yes I have drained down this system before) undone copper underneath the pump (so entering pump) and no water flowing from there either ( the pump is on the return pipe) - plenty of water flowing out from the radiator bleed valve when I open it in the airing cupboard hot press so no blockage or air from tank to airing cupboard so thats one thing - so I reckon the blockage or air lock in pipe from airing cupboard to outside boiler somewhere .

 

[Johntheo5]

You will have to do a lot of flushing then, .maybe use mains pressure