converting gravity fed HW CH to something better

That would be W or Y plan.

You don't normally add a pump but rather put a valve after it. Then when there is HW demand the pump circulates the water through the cylinder coil. When the CH demands it goes through the radiators.

You *can* implement with two pumps but it's a bit unusual.

Reply to
Andy Hall
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Well spotted. Normally the radiator circuit is 22mm and the pump tends to spoil any flow. However, you can have a valve operated by a light spring or a flap in the CH circuit. This stops natural "gravity" circulation unless the pump is running.

Generally when the pump runs there is still some cylinder circulation - just not as much as before.

That can happen.

With a gravity system the water is usually on a separate circuit to the pumped one but is fed to the upper connection. This promotes the natural circulation by convection in the gravity circuit,. "Gravity" is a misnomer. What is really happening is convection of the water between boiler and cylinder. Hot water from boiler rises to cylinder. Cool wate from cylinder falls to boiler.

This is why having a fully pumped system is better. You have complete control of both circuits.

Reply to
Andy Hall

They are connected in the sense that it's the same water.

They are separate in the sense that they start and end separately near the boiler

This is common in a gravity configuration. Boiler heat exchanger has one lot of water inside. There are four taps. Two are used to form the circuit with the cylinder and are in 28mm. The other two are

22mm and with a pump make the heating circuit.

Equally you could have one set of taps and a tee on those going to each circuit

If you do a system Y or W then you have a pump on that circuit and a valve after it.

You could also have two pumps - one on each circuit - although this is relatively unusual.

Honeywell's plans are based around their standard controls and valves and they also sell packs with all the bits needed. Their diagrams don't show the plumbing too well. There is nothing to say that you

*have" to follow their methodology but then you do need to understand clearly what the components are going to do.

The plans are for the convenience of installers and maintainers.

Reply to
Andy Hall

Thank you for your patience, I think I finally understand.

I know that I need to fit a valve to the cylinder and a cylinder stat. So far so good. This will involve running new wires: do I use 1.5mm^2 T&E? This will need to go to the controller, which is above the boiler. Now the direct route to the boiler is along the pipework! Is it ok to run the wire near the pipes, i.e. inside the same boxing? Obviously I would not tape it onto the pipes or anything daft, but I imagine these enclosed spaces still get hot. What temperature is standard T&E rated for?

I'm just a bit unsure about the pump. People have recommended I make it a pumped system. If the boiler had one outlet, it would be simple to put the pump before the tee, but as my boiler has two separate outlets, with a pump fitted on the 22mm CH side, how do I get the cylinder side pumped?

And of course, I'll need to drain down the system to fit the valve. Is it possible to fit a gate valve to the header tank outlet to make this easier in the future?

Thanks.

Reply to
nospam

This is OK, but you could run a cable with more ways if needed.

It's best to run them separately so not inside the same compartment unless you put in a barrier.

There are diiferent ways. One is to keep the existing 28mm pipework to provide the vent and fill arrangements. Then on the output side of the pump, assuming that it is in the flow path, fit a three way valve and run that to the cylinder.

Gate valves are a bad idea in general. full bore lever valves are the thing to use.

Reply to
Andy Hall

As Andy has said, you'd have either a W-Plan or a Y-Plan. W-Plan uses a

3-port diverter valve - which gives you either HW or CH but not both at the same time - usually with HW priority. With this system, you get no CH while the HW is being heated. Its ok if you've got a fast recovery cylinder with a big heat exchanger inside which can absorb all of the boiler output and heat the water quickly - otherwise not so good. Far more common these days is Y-Plan which uses a 3-port mid-position valve. At one end of its travel it gives you just HW, and at the other end it gives just CH. In the mid position it gives both at the same time.

You would have to make some plumbing changes to convert to a W or Y Plan - reducing the boiler connections from 4 to 3. You can leave the two returns as they are, but you need to blank off one of the flow connections so that the other one feeds first the pump and then the inlet of the 3-port valve. The CH and HW flow pipes then connect to the appropriate outputs of the

3-port valve. *But* you'll have to be extremely careful to make sure you always have an unrestricted path to the vent pipe - which may be very difficult - if not impossible - with your setup. [It's more usual - with Y-Plan - to have the pump and valve next to the HW cylinder rather than near the boiler, and for the fill and vent pipes to connect into the flow pipe just before the pump - but you can't do that because your CH circuit starts and ends at the boiler rather than in the airing cupboard.]

You *could* fit an additional pump in the HW circuit and, in your case, it may well be the easiest way of converting to a fully pumped solution. Again you'll need to put the pump somewhere where it won't restrict the path to the vent - maybe in the return rather than the flow pipe. You'll also need some logic - maybe involving one or two relays[1] - to ensure that the right combination of boiler and pump(s) are running, depending on the demand.

[1] I have a feeling that I worked out how to do a 2-pump solution without needing relays a year or two ago. If you're interested in pursuing this route, I'll try to find it.
Reply to
Roger Mills

You're unlikely to get gravity circulation through the CH circuit because it has a much higher flow resistance than the HW circuit - but it *may* happen. If so, you can get a valve with a weighted flap which shuts off the circuit unless the pump is running to provide a bit more 'urge'.

No - that's the right way round. It rises by convection to the highest point - the top of the cylinder - and heats the cylinder, cooling as it does so, on its way back down.

Reply to
Roger Mills

Yes they both use the same water. When you first fill the system, the water will flow down into the boiler from the F&E tank and then out the other side to the radiators. But once it is full, you have two loops which can flow more or less independent of each other. Think of it a bit like connecting two electrical circuits to the same battery. The same electrons flow round both, but you can switch them on and off independently.

See my other post re 2 pumps vs a 3-port valve system. A lot depends on where you're starting from!

Reply to
Roger Mills

I think I've answered that in another recent post.

Reply to
Roger Mills

1.5mm^2 cable will be fine as long as it's not *too* close to the pipes. You have to down-rate its current capacity when it's in a hot environment - but it's only going to be carrying about 3 amps, and has plenty in hand.

As I said in another post, you'd have to alter the pipework.

You could do - don't forget to open it again when you've finished! Or you could just stuff a cork in the F&E tank outlet from inside the tank to reduce the amount to be drained off.

Reply to
Roger Mills

Thank you both, for your replies. I don't like the sound of W-plan as it's either-or approach doesn't seem very useful; I don't know why anyone would want that.

I know you typed this but I'm going to type it back, just to make sure I have got it right:

At the moment I have four connections to the boiler CH in and out and HW in and out. If I have understood, I would need to keep one of the HW connections as this fills the boiler and also functions as the vent. presumably I keep the top connecion as the bottom connection would not work as a vent?

Then on the CH output I fit a pump (or rather leave the existing one there) and after the pump fit a three way valve to divert to CH, HW, or both.

That's not strictly true. At th boiler the CH pipes go down into the floor for the ground floor radiators but they also run up alongside the 28mm pipe, to feed the upstairs radiators. Could I not move the pump next to the cylinder and pump into the 22mm pipes upstairs?

I think it's worth adding a cylinder stat and valve when I get round to it, but I am still unsure about the benefirs of pumped HW. Does it just mean the cylinder heats quicker?

I don't know if I should have said this before but it's an oil boiler so we use economy seven to heat the water most of the time; that's why I think it would be useful to be able to have CH without HW.

Thanks.

Reply to
nospam

Limited output Combi. No hot water storage. Divert full power to water when needed.

Or two valves. One for CH and one for hot.

Basically that, and independence of tank siting, and smaller bore pipework with less heatlosses.

Its still marginally cheaper to use oil to heat.

Reply to
The Natural Philosopher

It's probably that diverter valves were invented before mid-position valves, but have largely been superceded by the latter.

Yes you could indeed, and this would be the best way to go if you're converting to a fully pumped system with a single pump. Not all systems have the CH pipes conveniently close to the HW pipes like that! So you could do this:

  • Blank off the CH flow connection on the boiler and remove the pipe which feeds the up/down distribution pipe, and blank off the end
  • Leave the CH return pipe connected to the boiler [If the pump is currently in the return pipe, remove it and replace it with a bit of pipe. If it's currently in the flow pipe, it will have been removed in the first action above, anyway]
  • You may need to change where the vent and fill pipes are connected in the airing cupboard, in order to get everything in. They need to be close to each other and *before* the pump, on the 28mm flow pipe
  • Fit the mid position valve above the pump, with the HW output connecting to the top of the cylinder coil, and the CH output connecting into the top of your CH up/down distribution pipe

It also means that the boiler doesn't need to keep itself hot for so long when you're just heating the HW, so it saves a bit of fuel.

If you don't use the boiler much for HW, and mainly want to be able to have just the CH on without the HW getting too hot, the C-Plan solution is fine and is by far the simplest to implement.

Reply to
Roger Mills

Sorry, you've lost me there. I see that 15mm pipe has a smaller surface area than the same length of 28mm pipe but isn't heat loss related to the ratio of surface area to volume? I would have thought larger pipes would have less ehat loss? Isn't that why 15mm pipes are more likely to freeze than 22mm ones?

What about the tank siting? Surely that feeds by gravity anyway?

I didn't know that: I thought they were about the same. But you never run out of electricity and never have to phone around for the cheapest quote and spend a morning waiting to let an electricity delivery man in.

Reply to
nospam

Sorry if this is a silly question: which CH pipe do I blank? I know the hot water relies on the hot water rising, so I assume cold water goes in at the bottom of the boiler and hot out at the top. So I blank the hot CH out pipe and take my CH and HW from the HW pipe? It's the

28mm HW pipe which vents so this should not be a problem.

Why can't I also blank the CH return and use the 28mm return for both CH and HW? I think it would be best to leave the old pipes in situ rather than remove them otherwise it means ripping up a lot of floorboards.

By the time I have drained down to fit the valve, i may as well move the pump at the same time.

Thanks again.

Reply to
nospam

I think here water heating is less than 5% of the total heating.

So it impacts little on the oil fill thing: we need that twice a year anyway.

In a modern flat of sound insulation with loads of people being anal about washing, it could of curse be far higher.

Reply to
The Natural Philosopher

I'm afraid there is precious little insulation here. We have insulated the loft but all the CH and HW pipes are run in notches cut in the joists just below floorboard level (22mm and 28mm below!) so there is no room for lagging. Any suggestions on how to insulate these hot pipes?

By the way, there is no cross bonding on all these pipes. The only earth wire I have found is one on the oil pipe. I assume the CH and HW pipes ought to be bonded at the boiler? I'll add that on to the list!

Reply to
nospam

"nospam" wrote

Absolutely! I had to re-program my parent's time clock recently and noticed that the hot water was timed to come on with the heating in the morning (for 3-4 hours). Thinking this was a mistake, I reduced this to 1/2 hour like my pumped system. The next day they rang to complain of no hot water! Had to increase the time back upto 3 hours IIRC as they have gravity circulation from back boiler.

Phil

Reply to
TheScullster

The 3-port valve needs to be on the flow side (rather than the return) of both circuits - so it's the CH flow pipe which you need to disconnect from the boiler, and connect (further along it!) to the CH output from the 3-port valve instead. I would expect it to be the higher pipe on the CH side of the boiler, but you can easily tell by feeling the pipes when the heating has been on for a few minutes - the flow pipe will be a lot hotter than the return.

I never suggested ripping out lots of pipe - just removing a short piece immediately by the boiler. The pipes which go under the floor for the downstairs rads and up near the 28mm pipes for the upstairs rads need to remain intact. If you want to blank off both CH connections on the boiler, and connect the CH return into the 28mm return pipe in the airing cupboard, that's ok. My rationale for not doing that was to minimise the distance which the water has to flow.

If you think about it, on the flow side, all the flow for HW and for both upstairs and downstairs CH will go up to 28mm flow pipe to the airing cupboard. After the 3-port valve, the CH flow will split into 2 - with the feeds to the upstairs rads going under the upstairs floorboards, and with the feed for the downstairs rads coming down the 22mm pipe which it currently goes up. No problem with that, and no way of avoiding it if the pump and valve are upstairs.

On the return side, the return from the downstairs rads currently comes back to the vicinity of the boiler, where it meets the return coming down from upstairs, and connects into the boiler. If you blank off this connection, and connect the return upstairs instead, it means that the return water from the downstairs rads has to go back upstairs in order to come down the 28mm pipe rather than going straight into the boiler at downstairs level. I don't see the point of that!

Reply to
Roger Mills

Thank you for your explanation. I quite agree it would be silly for the water from the downstairs rads to go up and then down again. I'm not sure that's what I was thinking of when I posted; I think I meant using the 28mm pipe downstairs but now I think about it again, it seems silly putting a tee piece in this and connecting the CH pipe to the tee, when I get the same effect leaving it connected to the other side of the boiler without doing any work!

What I will do is on the 28mm from the boiler, fit a tee piece in the airing cupboard. The one end of this will run into the loft as the vent. The other connection will go to the pump and then there will be either one three port valve to CH and HW or two 2 port valves, one each for CH and HW. (Not forgetting cyclinder stat etc).

Thanks for your help over the last couple of days.

Reply to
nospam

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