Central Heating Gravity system (again) -how to get to zone valve or fully pumped

[Clive M]

Right, been up in the lofts today and had a good look at how everything is plumbed. Can anyone advise if they would go with zone valve and keep a semi gravity system - or convert to fully pumped (and how - placement of valve etc)

Current system is setup as follows.

Boiler downstairs utility - two 28mm pipe flow and return come out of the boiler, through the downstairs loft and upwards to the main loft upstairs (cylinder). One pipe enters the top of the cylinder coil via a T piece which then carried on the the curved overflow pipe which is over the expansion/header tank. The outlet of the expansion tank goes to the bottom of the cylinder coil via another T piece and then connects to the pipe back to the boiler. Thus the two gravity HW pipes from the boiler also serve as the header refill.

In the downstairs loft there is a T piece fitted to the 28mm pipe taking a

22mm feed which is connected to the pump which then connects to the heating flow circuit. There is also a T piece fitted to the main 28mm return pipe which is the return from the heating system.

For ease of wiring any valve etc would need to be fitted in the downstairs loft near the boiler (rather than near the cylinder). - but as I see it this would then block the heater tank feed, on either a 2port valve or fully pumped system.

Is it possible to add either a 2 port valve, or convert to some sort of fully pumped system to the HW without serious modification?

Let me know if you need any more info.

thanks

[Set Square]

Your best bet is to keep your semi-gravity system, but to convert it to a C-Plan - which stops the gravity flow once the HW is hot enough and turns off the boiler whenever neither HW or CH require heat.

You *must* have a clear route from the boiler to the expansion pipe with no valves in the way. You must therefore put the valve in the short bit of pipe between the T-piece and the connection to the top of the cylinder coil.

If you want a fully pumped solution, you can go for an S-Plan by putting another 2-port valve in the heating circuit.

It would be very much harder to go for a Y-plan because this would require the 3-port valve to be installed in your downstairs loft - where the CH & HW circuits split - and you would have to re-pipe your overflow all the way from the boiler side of this junction.

Have you considered conversion to a non-vented system? If your boiler is suitable (have a look at the manual) you could get rid of the feed and expansion tank and replace it with a pressure vessel and filling loop. You would then have a lot more flexibility about siting your zone valves. You could probably even have a Y-Plan with its 3-port valve if that's what you really want.

[Clive M]

As I though. HW recovery rate is ok, so main reason is control of HW temp.

This would mean that the 2port *would have* to be fitted in the main loft on the cylinder which would be a pain in the a**. I was already going to use a RF tank stat to get from the boiler to the main loft.

As I suspected - virtually impossible to add a new pipe -

>

[Set Square]

Is your problem that of having to run cables to the valve located next to the hot cylinder? If so, there are obviously pipes which travel the required route. Can't you run the cables alongside the pipes?

One thing I forget to mention in the previous post: If you *do* decide on an S-Plan fully pumped system - by putting an additional 2-port valve in the heating circuit - you will, of course, have to move the pump into the common section of pipe near the boiler, before the circuits split.

[Clive M]

The boiler is in the downstairs utility - and the cylinder in the upstairs loft. Getting a cable back to the loft means going through both two floors and across the width of the house, which would be very difficult - hence the preference for a RF tank stat. It appears however that this is not possible with current plumbing.

an S-Plan fully pumped system - by putting an additional 2-port valve in the

common section of pipe near the boiler, before the circuits split.

Of course - going to S plan however would still mean that the HW valve need to be fitted in the upstairs loft - and prevent a RF tank stat being used.

[Set Square]

There's no problem in using an RF tank stat - but I haven't come across any RF zone valves with remote motor controls and volt-free contacts - which is what you would need to avoid having to run cables to it.

[John Cross]

What about using a RF tank stat, and a seperate wired stat and zone valve locally on the cylinder.

At the preset temp the wired stat could close the zone valve, and the RF stat report back to the boiler to switch off.

By using two stats you may have a slight difference in switching temps (which may cause a little bit of cycling) but it should work ok.

[Set Square]

It would get round the wiring problem - but it's a hell of a fudge!

The idea is supposed to be that the stat opens the valve, and that the volt-free contacts on the valve turn the boiler on when the valve is open - thus providing a sort-of closed loop control system. What you're suggesting would be open loop. If the two stats switched at different temperatures (which they inevitably would) you'd either have the boiler running with the valve closed (may not matter on a gravity system) or you'd have the valve opening but no boiler action (unless the boiler was on for the benefit of the CH).

In fact, it probably *would* work - but try explaining it to anyone needing to work on the system!

[Mike Hicks]

There is a way around it.

Use a Danfoss RF cylinder stat and 2 Danfoss RX1 receivers (one at the boiler and one at the valve)

When the Stat swichs both RX1 receive the signal and control the boiler and valve seperatly but at the same time.