Mid-Position 3 Port Valve - Hot Water (A) position & OFF - but HW flow to boiler?

[Clivedodd]

I have just fitted a 3 port drayton MA1 valve, room and cylinder stat

- it's all working very well but I have one small problem. The indirect water pipework remains hot long after the boiler and pump have shut down - I investigated and shut-off an old gate valve to prevent water flow (the MA1 3 port valve was in the unmotored A position), anyway this stopped the pipework remaining hot. It appears that the hot water cylinder is inducing a water flow in the indirect pipework - does this matter? well the tank is lagged so what's the point if it's hot water heat is being slowly dissipated by the induced water flow?????? Has something failed in my system or should I have gone for a twinzone system instead???

[BillR]

I seemed to get this is my system too with 3-port valves. The 3-port valves (Honeywell) never seemed to last that long anyway, so in the end I bit the bullet and changed it to an S plan. Imho 3-port valves should be avoided, they are a compromise and have a design fault whereby the motor coil is constantly energised in a certain system state. Neither do they give you volt-free contacts which you need for some modern boilers.

[IMM]

You referring to a mid-position valve. You should have used a 3-port diverter valve and fit a quick recovery cylinder.

In many cases the whole valve and brass casting is the same as a normal 2 ports and a diverter. Many two-port valves have a brass blanking plug under the body, that requires a large hex key to undo. Remove this and insert a 1" MBSP x 22mm brass compression fitting and hey presto a 3-port valve. That is what some makers do. Drayton certainly do, and have the same body casting for all their domestic valves even the 3-port mid-position. The ball mechanism side is the same for all the 2 port and 3-port diverter valves.

Go to B&Q and look at the Drayton's on show (a good valve), the mid position valve has a 1" MBSP x 22mm brass compression fitting screwed in where the plug was. You can buy a cheap off the shelf 2-port (£32 in B&Q) with an integral end switch (most diverters don't have end switches being a special order for some strange reason) and insert for a few pounds the 1"x 22mm fitting or 1"x28mm fitting. Hey presto a 3-port diverter withy an end switch and much cheaper too.

[Clivedodd]

One and all, thanks for all the information - especially that this convection behaviour is not confined to just me. As a DIYer (fast becoming C/H engineer) I'm surprised that the 3-port mid position valve is sold seeing as it has the Port B motor drawing current (with no CH or HW demaand) issue aswell as the convention waste of hot water issue. I wish I'd gone for a twinzone double 2 port valve system (lower failure rates of the valves and closed if not energized) but my

3 port mid is now working (well as well as it's designed to).

I've seen some posts about W plan 3 port diverter systems not being the best system and users changing to Y plan. So not convinced on this strategy.

Me thinks I'll either put up with the system as is OR probably use the old Honeywell 2 port valve (I was upgrading my old system without room or cylinder stat and inability to have independant CH only by using a Simp-L-Fit packaged BiFlo solution from Invensys/Drayton). Anyway, I fitted an ABV so I guess I can install the old 2 port valve in the pipe between the Port A of the Drayton 3 posn valve and the cylinder - ideally only being energized (i.e. open) when the pump/boiler is running and the 3 pos is in either A or A+B? Not sure I can figure out the wires for that (only 3 used to be connected - L, N, E), so maybe I'll just plug these into the Pump/Boiler terminals (OK the 2 port would be open unnecessarily with a CH only demand). When the 3 posn fails then I could buy another 2 port and switch to a twinzone system (which I wish I'd gone for now I know something more about this subject). Anyone any ideas on ideal wiring of my 'stop convection wasting heat energy' 2 port valve?

Thanks for all the help so far, very useful