Gravity hot water

31 Mar 2006
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United Kingdom
I have an old fashioned heating system at my house, but it's really reliable with no PCBs or the like to go wrong, so I have no intention to replace the boiler.

At the moment I have gravity hot water and just switching a pump on and off to control the heating which doesn't give much control overall.

As part of some renovation work I'm splitting the heating into three zones using a two port valve for each area.

I was wondering if it's safe / going to work whilst I've got the system drained down, to fit an extra zone valve in the gravity hot water pipe work and maybe with a cylinder stat too to control the hot water more effectively.

Any advice is greatly welcomed.
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You may, or may not be aware of this:
Sundial C plan page 13 (?)
Right I've had a look at the system. The gravity circuit from the boiler to the cylinder coil is on 22mm pipework.

Tee'd into the bottom connection of the cylinder coil is the 15mm pipe from the bottom of the F&E tank in the loft. Tee'd into the top connection to the cylinder coil is the 22mm vent to the loft.

I would like to fit a zone valve to one of the pipes as they leave the top of the boiler. if so, which pipe should it be fitted to?

Also I understand our gravity circuit is a bit on the small side. Is a 22mm zone valve likely to cause a restriction? Should I use a 28mm 2 port instead?

Here's a couple of pics of the boiler area. I'm also going to replace the pump and move it from under the floor to the boiler cupboard. Is it ok to leave it in the return pipework as it currently is, or would it be better in the flow pipe?




Sorry the pics are on their side. The forum software has decided to rotate them for some reason :rolleyes:
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Ok maybe this was too many questions for one post! My main question at the moment is regarding the pump.

Would it be best to keep it in the return pipework as it is now, or is it better moved to the flow pipe?

Thanks for reading!
Better off using a tapstat for the hot water circuit if you ask me. Much easier and sticks to your simple system.

Don't move the pump if it's working fine as it is. No advantage.
Thanks for your reply. I definitely want to move the pump from under the floor. I had a problem with it earlier in the year and it was a royal PITA to work on it where it is.

If it's better left in the return then so be it. Would you put it above or below the magnaclean?

I think I'll leave the DHW as it is. I'm not sure I'll see a return on the work to zone it properly. The boiler stat seems to do an ok job of regulating the temperature. What is a tapstat? I've not come across one of these before.
A Tapstat is a thermostatic valve. It goes on the return pipe where it comes out of the cylinder. When the cylinder is hot, detected by a small sensor on a capillary tube, it closes. It can be used when there is no valve and thermostat to control the primary circulation. The boiler will continue to fire up for short periods which wastes energy.

Retail price is round about a ton. Made by Drayton. Not often used, even if you can still get one. It somewhat resembles a thermostatic radiator valve with remote sensor bulb.

If you have an old cylinder, it might start to leak when you put a big spanner on it.

It would be more efficient in summer to use a cylinder stat to control the on/off of the boiler for HW demand. In winter though the cylinder would always be heated on your gravity circ unless you add a motorised valve.

Unpumped gravity circ is quite slow to warm the pipes and cylinder.

Time to move into the 1980's, perhaps.
change that pump as well its a got to be late 1970`s early 80`s.
And if your going to hassle of making it separate zones and thinking of adding a cylinder stat and HW motorised valve why not just make it fully pumped ?

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