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One for the heating engineers

diybry

diybry

pfm Member
I've recently fitted a Wiser control sytem to my fairly conventional oil fired cenral heating system, Y plan with mid position 3 port valve.
I've found the control provided by this sytem to be excellent. It provides individual programmable temperature control to each room using programmable rad valves and hot water via an app on my phone, and is highly recommended. But that's not the point of this post. (I have no connection with Drayton)
I'm thinking that as the Wiser system switches off the boiler when there is no call for heat, and hot water is controlled independantly, is there any need for the 3 port valve?
If and when the 3 way valve fails, I am thinking I could replace this with a single, more reliable zone valve for the hot water only, as each rad is now individually controlled by the wiser valves.
I would also add a modulating pump, to ensure that the pressure is matched to demand in the event of low demand
Have I missed anything here?
 
You can't do away with the three port valve you can install another motorised valve and make the system an S Plan however.

But there's no point in doing that.

A Y plan and an S Plan means that you have independently timed control of the heating and hot water circuits ie two systems both working separately from each other, each motorised valve or the mid position valve brings on the boiler to heat each system by employing a room thermostat and a cylinder thermostat, there's a micro switch in the valves which either opens or closes the valve or moves the mid position valve to heating or hot water or mid (both) when there's a call for heat from the timer and or the thermostat (not the boiler thermostat).

The system you have, if it's like Honeywell's Evohome system, can have multiple heating zones but you still need to be able to control the heating circuit.

You could just stick a motorised valve on the cylinder and make that a separate zone but that would involve an alteration to the pipe-work and there really isn't any point to that IMO.
 
Thanks Twotone, the specific issue i will have when the mid pos valve gives up, is access to it. It's pretty well boxed in. Ive improved the ventilation to lower its op temp but it will fail one day. I was thinking that if I fix it in centre posn to allow flow to both tank and rads, then put a motor valve on the HW coil, the wiser system can control the valve for DHW and the rad valves independently.
What do you think about modulating pumps? are they worthwhile?
 
Putting a mid position valve into the manual mid position and fitting a separate zone valve is just a bodge.
Why is it so inaccessible? It was accessible when it was fitted was it not?
 
diybry said:
Thanks Twotone, the specific issue i will have when the mid pos valve gives up, is access to it. It's pretty well boxed in. Ive improved the ventilation to lower its op temp but it will fail one day. I was thinking that if I fix it in centre posn to allow flow to both tank and rads, then put a motor valve on the HW coil, the wiser system can control the valve for DHW and the rad valves independently.
What do you think about modulating pumps? are they worthwhile?
Click to expand...

The problem is when the valve fails normally you would put the valve into the manual/mid position which would enable you to temporarily have heating and hot water via the cylinder stat but once the cylinder gets up to temperature then the boiler shuts down and you start to lose the heating so to get round that you have to remove the cylinder stat from the the cylinder so that the stat is calling for heat 247 but that means you will have the boiler on 247 and the hot water will be constantly hot but you can get away with that until the valve is replaced by simply switching the whole system off and letting it cool down then switching it back on again and so on so simply installing a two port motorised valve at the cylinder, as you propose, would mean an additional cylinder stat and additional wiring back to the boiler which is pretty pointless (because your original cylinder stat would still be calling for heat and you would have no control over the heating circuit due to the faulty motorised valve) when you can simply replace the valve.

With some of the newer motorised valves you don't even have to drain the system you can just replace the actuator/motor head but sometimes you would be better off just replacing the entire valve as the ball can stick inside the valve.

I don't know the Drayton system but I suspect it will be similar to the Evohome system, you can buy a pack that includes two wireless relay boxes and a wireless cylinder stat however you would need to install a motorised valve to control the hot water if you didn't have one, I presume Honeywell expects the system to be either a Y or an S plan.

https://theevohomeshop.co.uk/honeyw...ell-evohome-wi-fi-connected-value-pack-a.html

Regarding modulating pumps I'm not a fan, I much prefer the old fashioned Grundfos 15-60/15-50 which you can still buy (copies) on Ebay for about £60 but if the system needs a modulating pump or if the customer wanted one then I'd install one for them, it all depends on the system to be honest.

Tony
 
First class advice again Tony.
Sorry if I appeared a little grumpy earlier but the shock of watching our politicians behaviour yesterday was beyond my comprehension.

Bloss
 
Thanks guys. Zone valve access- access was reduced during a garage conversion.
As stated, fixing the valve in the centre position would be a bodge. Ideally I'd prefer to remove it all together
To explain better my rational of how the system may work without the valve: For CH, as the old room stat is no longer used, replacement of the valve with a tee would result in flow to all the rads100% of the time the system timer is calling for heat.individual time and temp control of each rad is provided by the individual radio controlled rad valves. When all valves demand is satisfied the central wiser control unit shuts down the pump and boiler, (unless DHW is demanding heat as below.)
DHW timing is controlled separately by the wiser control unit, which also takes a signal from the existing tank stat and shuts down the boiler and pump if no demand for heat. (Unless CH is demanding heat)
So, my thinking is that a simple zone valve on the DHW primary coil, powered by what was the DHW demand supply to the 3 way valve, would allow timed thermostatic control of the DHW.
I hope I've explained this clearly this time!
 
You’ll really need to speak to someone locally who can assess the heating system pipe-work.

You will need a bypass between the two port valve for the cylinder and the heating circuit and you’ll probably need to move the pump position too and possibly the cold feed from the feed and expansion tank presuming the system is an open vent system and not sealed.

You could install a Drayton Cytrol valve on the return to the cylinder but they’re rubbish and I think that they’re only intended for gravity primaries and are also only available as a 28mm valve which isn’t a big deal but that would be an even worse bodge.
 
diybry said:
Thanks Twotone, the specific issue i will have when the mid pos valve gives up, is access to it. It's pretty well boxed in. Ive improved the ventilation to lower its op temp but it will fail one day. I was thinking that if I fix it in centre posn to allow flow to both tank and rads, then put a motor valve on the HW coil, the wiser system can control the valve for DHW and the rad valves independently.
What do you think about modulating pumps? are they worthwhile?
Click to expand...
We have a system with a three way valve, not quite the same as yours, however the it has been in operation for 22 years and has not failed, it operates twice a day for about 8/9 months of the year. There is something to be said for keeping heating systems as simple as possible, so I wouldn't use modulating pumps - -just another complexity. I would also try and find a way of making the system accessible for maintenance...removable panels or covers....best with just two screws.
 
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