cylinder thermostat

[1650772]

I want to install a cylinder thermostat on my gravity fed hot water system. From what I have read I will need to put in a 2 port zone valve between the cylinder and the boiler. Does the thermostat just need to control this valve or does it need to tell the boiler to turn off (if so won't that turn off my central heating too???).

 

[ChrisR]

We'd need full system details to answer that. Boiler, other valves if any, timer/programmer, + anything else you can tell.

 

[1650772]

Pretty sure that there are no other valves. Programmer is a Landis & Gyr RWB200. The boiler is a Potterton and is fairly old (at least 15 years). I can't find a model number for it.

 

[stevewilliams]

Yes I'm also looking at this option to improve the controllablity of my system and prevent back circulation (see my posting - anti-gravity valves).

I've found a good diagram (page 138) of exactly this in a book called 'How to fault find and repair central heating' by K G Nathan - don't go out and buy this because you can read the entire thing at www.helpmate.co.uk. (or as I did; borrow from my local library) It's written in a bizarre English and I can only assume the proof-reader was dyslexic or the word-processor was missing some vital keys but you can get the gist and the diagrams are very clear.

A plumber has told me that the two-port valve must not block the cold feed or the hot vent so the diagram's position of the valve in the flow after the boiler but before the vent is dangerous apart from that the diagram is sensible according to him.

The only other advice I was given was to try and use the same manufacturer's kit all the way through for ease of wiring.

Steve

 

[ChrisR]

I've looked at that site and not found "PAGE 138". As Isee it your options are acopmplete conversio to a fully pumped system, a 2 port in the short bit of pipe between where the vent is and the cylinder, or a Cyltrol type valve. That's a non-electric valve which shuts at a certain temp.

 

[stevewilliams]

Sorry about the reference - the index checked out with my hard copy and I assumed it was complete.

Checkout this webpage for the same wiring diagram www.gasman.fsbusiness.co.uk/images/cpl.gif

This is the system I've decided to install alongside my solar to prevent reverse circulation through the existing 28mm hot water flow and improve controllabilty (preheating in winter)

Steve Wiliams

 

[ChrisR]

That looks like standard outdated C plan! - see

http://content.honeywell.com/uk/homes/systems.htm#C Plan

which doesn't conform to building regs now because the water-heating is inefficient. Also I see nowt to stp the water going backwards specifically. You can get gravity operated swing check valves if thats what you need.

You still haven't said what your boiler is so we don't know if you have to accommodate pump overrun or a system bypass valve. Get it wrong and your boiler will overheat

 

[stevewilliams]

Mine's a very old Camray oil boiler which is on borrowed time and is probably extremely inefficient but kicks out gravity flowing hot water over 7 metres from my boiler room very quickly albeit with plenty of heat loss along the way - surely though, when the two-port valve is switched off (and if I fit it into the flow next to the cylinder - this does not interupt my vent by the way) this should stop reverse circulation up this pipe?! - my flow pipe feeds into the hot water cylinder from above hence my problem losing heat rapidly from the cylinder when the solar coil is heating the water.

Thanks for the advice.

Steve Wiliams

 

[ChrisR]

Yes - though they have a "proper" flow direction which tends to keep the valve closed when it's closed, most of them will work backwards for a low pressure. Use one which has a rubber ball shoved int' ole rather than the ones with a rotating D shape held by a weakish spring. Honeywell in other words, thoughthe 28mm you'll want is disproportionately expensive.

I've got about 6 different makes of 2port valve - I'll have a butchers to see if any of the others uses a strong mechanism. Drayton might be OK...

 

[stevewilliams]

Many thanks for that Chris - yes it seems a bit pricey - around £60 from my local 'discount' plumbing outfit.

I've just realised that Ive hijacked this converstaion - the original query about the hot water cylinder came from someone else. Come in number 1650772 it was your question!

Thanks for all your help - someone else has suggested to me that the hot water drawoff pipe leaving the cylinder should be at least twice as long horizontally as it is vertically before teeing off to the vent as this is another potential source of significant heat loss. What are your thoughts o this?


Steve Williams

 

[ChrisR]

at least twice as long horizontally as it is vertically <<

SOunds likea bit of an old wives tale. You DO get convection currents which is why you don't go straight up to the vent. Most of the shower pump manufacturers would have you take the hot outflow up at 45 degrees so youcan connect pump feeds on the underside (which doesn't work unless the cylinder feed is enormous).

Just insulate the b***dy thing!

Sorry havent looked at valves yet!