Vented Hot Water Cylinder Without Vent Pipe!

[SK_London]

After calling a plumber to look at our leaking power shower he discovered that there is no vent pipe coming off the hot water cylinder . The cylinder is an old indirect vented cylinder heated from the central heating boiler and has a secondary electric immersion heater that is disconnected.

Upon further investigation there is a vent pipe going in to the Cold Water Tank in the attic but is has been cut halfway down. We think that about 20 years ago the hot water cylinder was moved from the ground floor to the 1st floor and in doing so the plumber decided not to reinstate the vent pipe. Although this has been the case for over 20 yrs we have been told this is very dangerous and must be addressed.

The obvious things to do is to reinstate the vent pipe but the path would be very tricky (which is no doubt why it was never done!). So a second plumber suggested installing an expansion vessel to the existing cylinder. Would this actually work with this kind of cylinder and would it be compliant?

Has anyone come across examples of such cylinders without vent pipes from this period?

 

[SJB060685]

Some pictures would help. No vent is dangerous, are you sure it isn't tapped in somewhere?

 

[SK_London]

Some pictures would help. No vent is dangerous, are you sure it isn't tapped in somewhere?

Thanks for this.
I am pretty sure it's not tapped in because if you follow the old vent pipe that enters the top of the cold water cistern in the attic it comes to an abrupt end about 2m down. Will try and take some photos and post in the next 24hrs

 

[Stigster]

I'm afraid an installing an expansion vessel is not at all the right thing to do for this type of cylinder. The cylinder must have two paths for expansion, one being the cold feed from storage cistern to cylinder and the other is the vent. There are no other acceptable options. Because there will be an isolating valve on the cold feed, if this were ever to be closed and forgotten to re-open, when the cylinder is heated there will be nowhere for expansion to take place. That is a potentially very dangerous situation.

An open vented cylinder absolutely must have an open vent fitted and there's no way around that.

Your options are to have the vent re-instated, as long as you are absolutely certain the vent isn't tee'd in to the hot distribution pipe elsewhere and is actually in place, or you could ditch the cylinder altogether and install an unvented cylinder, providing your cold supply pressure and flow rates are within manufacturer's specifications. Normally that's a minimum 2 BAR pressure and 20-25 litres per minute flow rate. Different manufacturers have slightly different requirements but that's the ball park figures.

As SJB says, some pictures of the cylinder in its location and all associated pipework and pictures of the cold water storage cistern and pipework would be very helpful for us to help you.

 

[SK_London]

Thanks for the advice so far.

Attached are a few photos of the cylinder and the cold water cistern in the attic (by the way the capped 15mm hot water pipe coming off the top of the cylinder was the feed to the leaking power shower)

I looked again in the attic today and discovered that the 22mm vent pipe going into the cistern is not cut as previously reported. But where it actually goes is anyone's guess.

So I guess it is possible that the vent pipe is tied in to the hot water feed from the cylinder somewhere lower down. So two questions:

1) How can I work out where this vent pipe goes (without ripping up walls and floors boards) and if it is tied in to the hot water feed from the cylinder?

2) If the vent pipe is tied in to the hot water feed below the level of the cylinder is that not also a problem? My understanding is that a vent pipe must come out from the top of the cylinder and continue constantly upwards to the cistern.

Thanks again for any tips.

 

[fixitflav]

Thanks for this.
I am pretty sure it's not tapped in because if you follow the old vent pipe that enters the top of the cold water cistern in the attic it comes to an abrupt end about 2m down. Will try and take some photos and post in the next 24hrs

I would guess it's very unusual, and perhaps against the regs, but only potentially dangerous if the cold fill valve is closed. While that valve is open the pressure can't exceed the head from the CWST.

 

[John.g]

Drop the level in the CWST 6 inches then cut the vent pipe a few ins higher than this and start re establishing the CWST level and if water starts coming out of the (cut) vent then at least you know that it is connected somewhere to the system and giving another expansion path.

 

[SK_London]

Thanks John.g for the tip on how to check if the vent pipe is connected somewhere. If the vent pipe is indeed connected somewhere below the cylinder and hot water flows into the CWST in the test you describe, then can I assume that the system is safe? I was told that the vent pipe had to come out the top of the cylinder and only travel upwards to the CWST....

 

[Stigster]

If you have a wet-vac or access to one I'd use it to try to draw hot water from the end of the vent in the loft. If you can pull hot water there then you'll at least know that it's connected.

 

[Chuck]

Attached are a few photos of the cylinder and the cold water cistern in the attic (by the way the capped 15mm hot water pipe coming off the top of the cylinder was the feed to the leaking power shower)

There are several 'dead legs' in the pipework that need to be eliminated. There's a risk that legionella will colonise them.

 

[Stigster]

At least the dead leg is right at the top of the cylinder where it's hot but still I agree. That wants cutting out and simplifying.

 

[John.g]

[/QUOTE]

Thanks John.g for the tip on how to check if the vent pipe is connected somewhere. If the vent pipe is indeed connected somewhere below the cylinder and hot water flows into the CWST in the test you describe, then can I assume that the system is safe? I was told that the vent pipe had to come out the top of the cylinder and only travel upwards to the CWST..

If the above (proving) is done then the system IMO will be safeR but may not meet regulations, another reason for a continuously rising vent is that it may be difficult to clear air locking if the CWST ever runs dry.