Converting from gravity hw to fully pumped

[don]

I currently have a Potterton 16/22 boiler driving the central heating via a pumped circuit, and the hot water cylinder via convection.

I'm looking to move the hot water cylinder from its current location directly above the boiler (in the bathroom) into the loft. This will involve a much longer pipe run with a number of kinks, so I'm guessing I need to convert the system to be fully pumped?

I have basic plumping skills that have amounted to moving the odd radiator and fitted a new bathroom. The theory of what needs to happen sounds fairly straight forward, but is this a job I should be tackling myself, or should I leave it to the experts?

Does anybody have any references/links to information on the details of what is involved?

Thanks,

don

[Christian McArdle]

Yes. You need to decide whether you are going to pump the existing gravity circuit, or convert the system to an S-Plan or Y-Plan zone valve type system and use the old gravity circuit just for feeding and venting. You'll find loads about this within this newsgroup using Google.

Christian.

[Set Square]

Kinky

Does your loft have lots of headroom? Assuming that you're not going for a mains pressure hot water system, you'll need to get your cold header tank

*above* the level of the hot cylinder. This will need supporting *very* well - water is heavy stuff!

If you're going fully pumped with a single pump, you'll need both HW and CH to share a common flow pipe until after the pump - where the circuits then split using zone valves (S-Plan) or a 3-port mid-position valve (Y-Plan). [See

If you currently have separate circuits (4 pipes into the boiler) this will need changing.

If your boiler can stand it, you might consider converting to a non-vented (sealed) primary circuit - using a pressure vessel and filling loop, and getting rid of your small F&E tank.

[Brian Sharrock]

From installation in 1973 my ground-floor wall-hung Potterton 10-16 has been driving 28mm 'gravity' pipes up to an indirect hotwater cylinder in the loft. I'd guess the total height is 2 x 8'6" plus ceiling gaps say ~20 feet? The pipes also have a number of kinks as the heater is on an external wall and the tank is about fifteen feet into the centre-line of the house. As others have stated the cold water tank is mounted on an over-engineered timber structure towards the centre of the roof. Water is heavy.

[IMM]

It is about time you replaced all that and had it fully pumped. Gas has just been hyped up.

[don]

The intention is to try and get everything mounted above a supporting wall. The loft has enough head room for the cylinder plus a bit more. I was planning to get the water line for the header tank a few inches above the cylinder ... should I really be aiming to get the whole tank above the cylinder?

(Y-Plan).

was to put a 3 port valve directly after the pump and run a new 22mm pipe run straight upto the cylinder in the loft. This seems the simplest approach as it involves the least modification to existing pipe runs.

changing.

Yes, it has 4 pipes. Is it a simple case of capping off the existing pipe for the gravity cylinder? Or does it need to be a circuit with water in to stop the boiler over heating?

non-vented

Is the advantage here that you're losing the tank or is there an additional benefit?

Thanks,

Don

[don]

I'd be in a similar position as the cylinder needs to move towards the center of the house (for headroom reasons).

The other reason for the conversion is that we suffer slow recovery times (admittedly this could be down to the scale in the 30 year old hot water cylinder), and when the hot water is on in the summer the radiators become warm (I guess because of convection into the main central heating loop).

Don

[Set Square]

Yes! Consider the situation where you're running a bath and the header tank is less than full, because the mains feed can't keep up with the rate of hot flow. Once the level gets below that of the top of the cylinder, you'll be relying on syphoning to get any further flow.

Disconnect it at the boiler itself, and blank off the "hole" in the boiler.

If you *don't* do this, you will need to raise the F&E tank to a fair height

*above* the highest point in the primary circuit - which is now the coil in your hot cylinder. With the limited headroom available, you're in danger of having the primary circuit "pumping over". Also, you'll have to run a vent pipe all the way from the boiler side of your zone valves to the new F&E location. A sealed system would prevent pumping over, and would do away with the need for a vent pipe. It's also much better at keeping air - and the resultant corrosion - out. [The downside is that if you've any grotty old radiator valves, they may start leaking with the increased pressure.] Maybe a good time to replace all the valves with TRVs (on all rads bar one) and drainable lockshields at the other end.

[don]

Looking at the boiler, I think this would mean removing it from the wall as the pipes feed into the back of the boiler. This is something I was hoping to avoid doing as I believe it would mean getting in the professionals (as it would involve disconnecting the gas pipe temporarily.

Don