Water Tank and Expansion Vessel Overflow?

paperclap

Thank you both for your input.

Let me clear up some bits. Didn't realise it would be all this complicated! Some of the below may be helpful and some not relevant at all!

This is what we have:

• A conventional boiler.
• A hot water cylinder, located in the airing cupboard.
• A cold water tank, located in the loft.
• A pressurised heating system, with a gauge in the airing cupboard at a wonderful 1 bar.
• Our kitchen tap comes straight from the mains.
• Our bathroom tap is gravity fed. Our showers and bath tap are gravity fed. Pump or no pump, don't know... but they ain't from the mains! These are presumably supplied from a combination of the hot water cylinder and cold water tank.

Seems that little thing is indeed a PRV (Pressure Relief Valve). I'm presuming this is a safety feature installed to help an unvented (or pressurised) in the event of over pressurisation?

paperclap

It seems a 15mm to 21.5mm fitting doesn't exist!

Now I understand why the previous fitter used 22mm pipe...

Bendy_House

laurencewhymark said:

Thank you both for your input.

Let me clear up some bits. Didn't realise it would be all this complicated! Some of the below may be helpful and some not relevant at all!

This is what we have:

• A conventional boiler.
• A hot water cylinder, located in the airing cupboard.
• A cold water tank, located in the loft.
• A pressurised heating system, with a gauge in the airing cupboard at a wonderful 1 bar.
• Our kitchen tap comes straight from the mains.
• Our bathroom tap is gravity fed. Our showers and bath tap are gravity fed. Pump or no pump, don't know... but they ain't from the mains! These are presumably supplied from a combination of the hot water cylinder and cold water tank.

Seems that little thing is indeed a PRV (Pressure Relief Valve). I'm presuming this is a safety feature installed to help an unvented (or pressurised) in the event of over pressurisation?

Ah, item 4 explains a lot. Partly.

So this USED to be a vented system, and that small F&E tank USED to do the filling and expanding.

At some point a plumber converted it to a sealed, pressurised, unvented system, and this requires a pressure gauge (tick), a Pressure Release Valve (tickish), which should lead to a visible discharge pipe outlet (tickish), which should point either straight down close to the ground, or else bend back on itself and aim at the outside wall (um...). Ie, that pipe end should not be located where it might blast a jet of boiler water over anyone.

LwM, you are going to have to lift the lid on this mystery. See what's inside that small F&E tank.

paperclap

Bendy_House said:

laurencewhymark said:

Thank you both for your input.

Let me clear up some bits. Didn't realise it would be all this complicated! Some of the below may be helpful and some not relevant at all!

This is what we have:

• A conventional boiler.
• A hot water cylinder, located in the airing cupboard.
• A cold water tank, located in the loft.
• A pressurised heating system, with a gauge in the airing cupboard at a wonderful 1 bar.
• Our kitchen tap comes straight from the mains.
• Our bathroom tap is gravity fed. Our showers and bath tap are gravity fed. Pump or no pump, don't know... but they ain't from the mains! These are presumably supplied from a combination of the hot water cylinder and cold water tank.

Seems that little thing is indeed a PRV (Pressure Relief Valve). I'm presuming this is a safety feature installed to help an unvented (or pressurised) in the event of over pressurisation?

Ah, item 4 explains a lot. Partly.

So this USED to be a vented system, and that small F&E tank USED to do the filling and expanding.

At some point a plumber converted it to a sealed, pressurised, unvented system, and this requires a pressure gauge (tick), a Pressure Release Valve (tickish), which should lead to a visible discharge pipe outlet (tickish), which should point either straight down close to the ground, or else bend back on itself and aim at the outside wall (um...). Ie, that pipe end should not be located where it might blast a jet of boiler water over anyone.

LwM, you are going to have to lift the lid on this mystery. See what's inside that small F&E tank.

As it currently stands, the (now) expansion vessel does have the overflow pipe attached, and it does lead outside the property.

It is the cold water tank that has its overflow pipe lead straight into the soffit. God knows how or why. But, that should be an easy fix.

What the big problem now is, is figuring out the best way to tackle this 15mm pipe coming from the Pressure Release Valve.

Given a 15mm to 21.5mm reducer fitting doesn't actually exist, it seems the only option is to effectively replicate what has been done already (15mm to 22mm reducer, with push-fittings). But instead of having 22mm copper pipe sticking out to the outside world, I'll just use 22mm plastic pipe, just so it's nicer. Not ideal, given plastic pipe isn't UV stable, and push-fittings are expensive in comparison to solvent weld fittings... but can't see any other option! 

Alternatively, I use compression fittings with the plastic pipe, but grab some liners.

Bendy_House

STOP!

Until you know what has been done there.

Your system does not make sense as it stands.

A sealed/invented/pressurised CH system like yours NEEDS an Expansion VESSEL. That's the red cylinder shown in an earlier post, tho' a smaller 'flat' type is usually fitted INSIDE the boiler casing - IF it's a 'system' boiler.

So, first thing - do you have a big red thingy?

Second thing - make and model of your boiler.

Thirdly thing - where is the pressure gauge you mentioned?

The only way your current setup makes sense to me is if there IS an Exp Vessel somewhere, and the plumber then decided - in the most bizarre way - to route the safety discharge (which is supplied by a PRV) via that F&E tank. Ie, if the PRV is blown open (due to a fault that makes the boiler boil), then the discharge ends up in that tank, and then exits via the dodgy overflow. 

In which case, why do it that way?! Why not have the PRV discharging DIRECTLY outside as it should? Why put a F&E tank in the way?!

UNLESS, that tank is still being used to top up the system! But, it 'cannot' be, because that would PREVENT the system from being a 'sealed/unvented' type, and your pressure gauge would only show 0.2 bar max.

It doesn't add up. The components contradict themselves.

You MUST figure out what's going on before either you or a plumber sorts it. If you plumb for a plumber, then I'd be asking what the hell is going on with your system, and NOT be happy with just new overflow pipes. Just in case this system is as weird as it looks.

Oh, and rigid plastic pipe - the solvent stuff used for overflows - IS UV stable, as they all stick out into the sunshine!

But, if yours IS a 'safety discharge', then it SHOULDN'T. 

I wonder if the plumber thought passing the boiling discharge through a 'cooling' F&E tank was a 'clever' move?

paperclap

Yes, we have a big red expansion vessel.

Our boiler is a Potterton Profile 40e.

The pressure gauge is located in the airing cupboard, which is below the cold water tank and expansion vessel.

An F&E tank keeps being mentioned here, and I'm not sure why? We don't have one, that I'm aware of. Unless an F&E tank is the same as what we have and its a terminology mix-up?

The solvent pipe is UV stable, I know. But not sure the typical 22mm plastic pipe (used internally typically) is UV stable.

Just to confirm, are you suggesting the discharge pipe should have been connected directly to the Expansion Vessel... and not whacked on the end of the PRV?

Bendy_House

Aaarrgh! I'M the one talking cross purposes - sorry 

From your first photos, underneath all that lagging, I'd read you as having two TANKS, a CWS and an F&E. I see now that isn't the case.

Eek. Soz.

That PRV is coming from a red EV?! Underneath that lagging? Aaaaah.

Phew, that's better, and now the fact that a section of THAT discharge pipe is in 15mm COPPER is perfectly ok - in fact that's the normal size for a 'safety discharge pipe'.

BUT, that pipe MUST also be in copper. And it MUST exit to a safe point where it can also be observed. That means pointing to within a few inches of the ground, or bent bacl on itself aiming at the outside wall.

(The reason why 15mm is ok for this is because and discharge will be under pressure. Whereas the CWS's overflow will usually be a larger quantity and also at low - gravity - pressure. So 22mm rigid pipe required. Don't use plastic 'plumbing' pipe for this as the internal dia is less than rigid's.)

So, the main thing you need to check is whether that PRV discharge pipe is exiting safely, as described above.

grumbler

laurencewhymark said:

An F&E tank keeps being mentioned here, and I'm not sure why? We don't have one, that I'm aware of. Unless an F&E tank is the same as what we have and its a terminology mix-up?

Because you mentioned "an expansion vessel" located in your loft. Is it your "big red expansion vessel" actually? IMO, loft is a little unusual place for it, but this is possible.

With regard to the pipes, is "21" coming from the water tank in you diagram a typo? Is it 22 actually? If so, just use a 22mm push-fit (or compression) fitting and add a small piece of white plastic 22mm water (not overflow) pipe at the very end. You can replace a bigger part of the copper pipe if you wish.

For the pressure release branch you don't want to use an overflow pipe. The same 22mm (or, better 15mm) water pipe can be used, but as BH said, it has to be directed towards the wall or have a special cap at the and, unlike an overflow pipe.

You'll have to improvise if the pipe goes through the fascia.

Section62

laurencewhymark said:

It seems a 15mm to 21.5mm fitting doesn't exist!

Now I understand why the previous fitter used 22mm pipe...

grumbler said:

With regard to the pipes, is "21" coming from the water tank in you diagram a typo? Is it 22 actually? If so, just use a 22mm push-fit (or compression) fitting and add a small piece of white plastic 22mm water (not overflow) pipe at the very end. You can replace a bigger part of the copper pipe if you wish.

Wild guess...

Originally there were two tanks, a cold water storage tank and a F&E tank.  Both had 3/4 copper overflow pipes.

The cold water storage tank still has a 3/4 copper overflow.

The F&E tank has been removed and replaced with an expansion vessel.  The plumber had a (not so) bright idea to save time and materials by repurposing the ex F&E overflow pipe as the safety relief pipe.... cobbled together with 15mm and 22mm fittings, the latter of which probably isn't very secure on the end of the 3/4 pipe.

Laurence, you could replace the overflow pipe on the cold water tank, but you'll need to fit a new tank connector.  Be careful doing that as the tank appears to be either fibreglass (brittle) or asbestos (dangerous).

If the other pipe is the safety relief from an unvented heating system then I believe you will need to get a G3 or gas safe plumber to alter it for you.

grumbler

Section62 said:

laurencewhymark said:

It seems a 15mm to 21.5mm fitting doesn't exist!

Now I understand why the previous fitter used 22mm pipe...

grumbler said:

With regard to the pipes, is "21" coming from the water tank in you diagram a typo? Is it 22 actually? If so, just use a 22mm push-fit (or compression) fitting and add a small piece of white plastic 22mm water (not overflow) pipe at the very end. You can replace a bigger part of the copper pipe if you wish.

Wild guess...

Originally there were two tanks, a cold water storage tank and a F&E tank.  Both had 3/4 copper overflow pipes.

The cold water storage tank still has a 3/4 copper overflow.

...

Laurence, you could replace the overflow pipe on the cold water tank, but you'll need to fit a new tank connector.  ...

Why go through this hassle?

JG Speedfit Imperial to Metric Connector 3/4" x 22mm