S-plan+unvented cylinder with combi ?

[omph]

As the title suggests, is this do-able ? if so, how would one go about doing it. Would the DHW feed into the mains feed for the cylinder ?

 

[picasso]

Yes its doable, the 2 zone valves control the central heating water to heat the rads and/or the cylinder coil.

 

[Madrab]

Would the DHW feed into the mains feed for the cylinder

No, the instantaneous HW output from the combi, if needed, could be fed to a tap close to where the boiler was located. The CH flow and return from the combi would be used to heat the unvented cylinder as with any normal S Plan.

 

[omph]

No, the instantaneous HW output from the combi, if needed, could be fed to a tap close to where the boiler was located. The CH flow and return from the combi would be used to heat the unvented cylinder as with any normal S Plan.

How would that work in say the summer period where no CH is utilised ?

 

[DP]

How would that work in say the summer period where no CH is utilised ?

Think about it. Why would it not work?

 

[CBW]

How would that work in say the summer period where no CH is utilised ?

If you know how an s-plan works, then you’ll understand it’s not the central heating that heats up the cylinder.

 

[Madrab]

it’s not the central heating that heats up the cylinder

Eh? Sorry Chris but did I read that right? or is it just the definition of central heating?

 

[Madrab]

where no CH is utilised

the key is to what the words Central Heating actually means. The name central heating originally came from some wise chap who thought 'lets have a heat source located centrally within a given location to heat up water (could be part of an HVAC sys etc but for this example we'll keep it wet) in pipes and then radiate that hot water out to radiators in each area to heat up the space'. That same centrally heated hot water can also be diverted, via a valve, to a HW cylinder coil and heat that up, producing hot water at the taps.

If you don't run the central heating then it won't heat the water in the cylinder. That gives 3 options.

1) run the HW outlets required from the combi, kinda defeats the purpose of having a cylinder
2) heat the HW in the cylinder by an immersion element (leccy), much more expensive
3) have cold showers & baths

 

[CBW]

Eh? Sorry Chris but did I read that right? or is it just the definition of central heating?

What I mean is, the central heating doesn’t need to be on to heat the cylinder, obviously I know it uses the same circuit.

 

[omph]

the key is to what the words Central Heating actually means. The name central heating originally came from some wise chap who thought 'lets have a heat source located centrally within a given location to heat up water (could be part of an HVAC sys etc but for this example we'll keep it wet) in pipes and then radiate that hot water out to radiators in each area to heat up the space'. That same centrally heated hot water can also be diverted, via a valve, to a HW cylinder coil and heat that up, producing hot water at the taps.

If you don't run the central heating then it won't heat the water in the cylinder. That gives 3 options.

1) run the HW outlets required from the combi, kinda defeats the purpose of having a cylinder
2) heat the HW in the cylinder by an immersion element (leccy), much more expensive
3) have cold showers & baths

Makes sense. With the S-plan then, since the CH feed is used for both cylinder and rads, does that mean both can be heated at the same time ? is that advisable ? and how does one control the temps for hot water and the rads as there is only one control for CH.

 

[CBW]

Makes sense. With the S-plan then, since the CH feed is used for both cylinder and rads, does that mean both can be heated at the same time ? is that advisable ? and how does one control the temps for hot water and the rads as there is only one control for CH.

With a room thermostat for the heating and a cylinder thermostat for the hot water. Yes, both can be heated at the same time, this is why motorised valves are used, as they split off the heating and hot water or both on at the same time, same as a conventional or system boiler, just with the added hot water draw off being used at one outlet

 

[omph]

With a room thermostat for the heating and a cylinder thermostat for the hot water. Yes, both can be heated at the same time, this is why motorised valves are used, as they split off the heating and hot water or both on at the same time, same as a conventional or system boiler, just with the added hot water draw off being used at one outlet

Would the wiring be the same for the combi as it is for the system boiler ?

 

[CBW]

Would the wiring be the same for the combi as it is for the system boiler ?

Pretty much. It’s only the switch live back to the boiler.

 

[Madrab]

how does one control the temps for hot water and the rads as there is only one control for CH

In the case of a system that is running say a cooler water temp for rads but needs to run hotter to get the HW up to 60Deg then Open Therm protocol (OT) can be used with smart controls. That will allow the system water temps to be controller directly at different times. Then it comes down to time planning whereby you are heating the HW mainly outside when the radiators are to be used. Combi's can use OT.

 

[omph]

In the case of a system that is running say a cooler water temp for rads but needs to run hotter to get the HW up to 60Deg then Open Therm protocol (OT) can be used with smart controls. That will allow the system water temps to be controller directly at different times. Then it comes down to time planning whereby you are heating the HW mainly outside when the radiators are to be used. Combi's can use OT.

The problem is I use weather comp with 24/7 low temp heating so managing the differing temps is a tricky affair. The combi is an annoyance since DHW turns off the heating.