I would like to have more contro over my heating system and to that end I have installed a 6x 7 day room stat. I now want to fit cylinder stat and zone valve for the HWS and re-wire the timing, but I have no installation space between cylinder and vent and feed for the zone valve. Are there any alternatives methods of achieving the above.
The valve does not have to sit next to the cylinder. In fact, it can be installed anywhere in the heating circuit. The only consideration you must have is from a safety point of view . A clear route must always be available to the expansion pipe for escaping steam and boiling water in the event of a boiler failure. This usually discounts fitting the valve in the flow side. Similarly, the valve must not restrict the feed of water from the header tank into the system.
I have just done a similar conversion.
I fitted a 2 port zone valve and small circ pump in the return pipe from the bottom of the cylinder coil.
When the tank stat calls for heat, it opens the valve, which in turn switches on the pump and and boiler signal.
This now heats up a cylinder full of water in 20 mins, then turns off the boiler. A big improvement on the old gravity system. It also prevents the DHW overheating when the CH is on continuously.
It is important not to restrict the vent / makeup section of pipework. In my case these were in the connection after the flow into the top of the cylinder coil. Which is why I put the control eqp into the return leg.
You can cut the hot feed from the boiler to the hot water tank at any point. The motorised valve doesn't need to be near the boiler - you can buy four or five core wire to extend the wire attached to the valve.