Hot Water Vent Pipe

[diynoob]

The hot water pipe from the boiler to the H/W Cylinder is slow to circulate. There's no pump, it works off gravity. The pipework looks messy, the tee for the vent pipe off the main pipe is in the wrong place. If I crack the nut, sometimes air comes out.

Does it make sense to move the vent pipe up in order to avoid air collecting in the H/W pipe?

 

[oldbuffer]

1. That pipework looks like 22 mm, whereas I'd expect a gravity feed to be 28 mm.
2. If you have a combi or system boiler, the pump will be inside the boiler.
3. It would make sense to move the vent. Replace the elbow with a reducing Tee and fit an automatic or manual air vent to a short length of pipe. You might need to bend the bit of pipe to get the vent upright.

 

[diynoob]

It’s an oil boiler. The last time it was serviced the engineer confirmed that the central heating is pumped but the HW is gravity and expected it to be a bit slow.

I’ll fit an auto air vent as you describe. I can’t understand why they piped it all the way up to the loft tank to vent?

Edit: I changed my mind, it's open vented so I won't replace the vent pipe with an auto air vent.

 

[Hugh Jaleak]

If the system is open vented that vent pipe needs to go all the way up and over the F&E cistern to vent, it is also a safety discharge in the event of the boiler malfunctioning and allows water, steam and/or excess pressure to release to atmosphere. Do not under any circumstances cap it with anything.


Slow circulation could be due to the 22mm primaries, I was always told they needed to be minimum of 28mm for gravity circulation. Possible there could be a blockage there too. Test with a magnet, if it sticks to the pipework anywhere round there, that is your problem.

 

[Madrab]

If the system is open vented that vent pipe needs to go all the way up and over the F&E cistern to vent, it is also a safety discharge in the event of the boiler malfunctioning and allows water, steam and/or excess pressure to release to atmosphere.

I read it like that to start with & then re-read @Hugh Jaleak, I believe (and sincerely hope) he is talking about the high bleed point for the primary flow into the cylinder coil.

 

[Hugh Jaleak]

I can’t understand why they piped it all the way up to the loft tank to vent?

I think we need to know exactly what the set up is before advising further, dont want you making a bad situation worse.

 

[diynoob]

It's a normal boiler, not a combi or system boiler. It's open vented with 2 tanks in the loft. I will leave the venting as is then if it's correct to vent to the loft tank.

There is a pump on the CH circuit but not on the HW. Is it advisable to add a small pump to the HW to speed thing up? A small inline pump would be easy to fit near the boiler.

 

[Madrab]

Are you sure it works off of gravity? I would be surprised that it would be given the primaries are 22mm. You may find you have a 3 port valve somewhere. What boiler do you have?

 

[diynoob]

It's an ancient oil boiler so there's no pump in it, the pump is on the CH pipes. I can see the whole run of the HW pipes and there is no pump. When the boiler comes on the flow pipe heats up very quickly but it takes ages for the return to heat up because the water circulates slowly. The engineers that service the boiler always look in horror at it and say that when it packs in they'll replace the whole mess with a system boiler.

For now I'm just looking to speed up the circulation of the HW pipes by changing pipework or adding a pump or whatever people recommend.

CH Pipes near boiler:



HW Pipes near boiler (no pump):

 

[oldbuffer]

1. Its in the wrong place to be the vent to the CWSC.
2. Given one pipe above the other it's almost certainly the primary coil, so adding somewhere to bleed air from the system shouldn't be an issue.

 

[diynoob]

1. Its in the wrong place to be the vent to the CWSC.
2. Given one pipe above the other it's almost certainly the primary coil, so adding somewhere to bleed air from the system shouldn't be an issue.

The HW cylinder has 2 coils (one from oil boiler one from oil Aga) and an electric immersion. As you say, I may well have incorrectly identified the vent (a heating engineer told me it was the vent to the loft tank though). I'll post some more pictures to give a clearer idea.

Firstly let's take a step back - would you expect the coils to go from top to bottom or side to side? I thought they went from top to bottom but I've turned the Aga off and it seems that the top left pipe is the boiler return because it's warm. Does this make sense? I'm starting to think one of the coils is leaking.

 

[diynoob]

If the labelling in the picture above is wrong, and the Boiler Return is as labelled below then there must be a leak in the coil or a blocked coil because the pipes at the bottom right are stone cold when the boiler is running.

 

[Madrab]

Do you have a label on the cylinder, something to identify it? That should help with id'ing the tappings and internals.

 

[diynoob]

Do you have a label on the cylinder, something to identify it? That should help with id'ing the tappings and internals.

There aren't any labels at all unfortunately. However I've traced the vent pipe and it does go up to the loft tank so I'm certain of that now.

I think I know what's been confusing me. The vent from the boiler feed joins up with the vent from the Aga feed. So hot water flows around these vent pipes from the boiler feed into the Aga feed. This makes the cylinder pipes hot to touch even when the Aga is off. With the Aga off I was expecting that the cylinder would have one hot pipe (boiler feed), one warm pipe (boiler return) and 2 cold pipes (the aga flow and return pipes), but that isn't the case.

 

[Madrab]

Where is the supply from the cylinder? Is that coming out of the top of the cylinder? There should also be a vent that should run from there up and over the CWSC.

Given that it's gravity fed primaries then having them venting themselves up to the CWSC isn't really that much of an issue, not a normal approach to join them though (are the returns joined too?). They may be joined as a bypass - is the aga solid fuel or gas? - the concern would be though that they could be shortcutting themselves with both trying to feed both coils.