C-Plan.. S-Plan... Drayton Wiser? Help :)

[longeggs]

Hello

We've just moved into a new (old, but new to us) house and I'm trying to improve the boiler & control that we've inherited (it needs replacing in all honesty but we've just spent all of our bunse on the house!).. The boiler is a bluebird 90/120.. Oil thing.. currently controlled via a Channel Plus XL H21 set to 'gravity mode'.

There's an unvented cylinder and the cydliner stat has been cut off and goes nowhere. Who or why this happened I dont know, but they're relying on the boiler stat set to 60c to gravity feed the cylinder tank. There is an old grundfos pump and a honeywell valve on the CH. It looks like this...

What I want to do is reinstate the cylinder stat which turns on a new valve on the HW side and control the whole lot with a Drayton Wiser (which aren't for gravity systems apparently).

So like this:

The HW side would still rely on convection since its not pumped.. but at least the Drayton can handle this.. maybe? Kind of S-Plan?

I want to keep the boiler because we can't afford a new one right now to be blunt.. but the current control (Channel Plus) is ****e, and as I say the unventeed cylinder has no thermostat currently. The pump needs replacing too and wiring in properly (it's currently plugged permanently into a socket, so is on 24/7 even without a CH demand... bonkers).

I think my plan is:
Drayton HW ON -> Cylinder stat -> HW valve -> Boiler ON
Drayton CH ON -> CH Valve -> Pump -> Boiler ON
(and on the Wiser, make it that whenever CH is ON, to also set HW ON, so that both valves are open and we beneffit from tank heating when the CH is on).


Sigh..
Any advice? Is my plan sound? Is the Wiser a bad idea since it's "not made" for gravity systems? I already bought the Wiser, but would I be better off with a Hive.. or something else?

I just need to get through Winter
Any help would be appreciated.
Thanks

 

[longeggs]

Could I remove one set of flow/return pipes from the boiler so I can do a fully pumped "more normal" s-plan ?

 

[CountryFan]

This doesn’t make sense. Are you sure it’s an unvented cylinder? If it’s is then I doubt it’s got all the necessary safety controls.

 

[longeggs]

It's 100% unvented and 100% doesnt have the necessary safety controls. It has a 90c over temp pressure relief valve, and a 3bar pressure reducing valve on the cold input but thats about it... thats why at a minimum I want to add back in the cylinder stat + add a valve to the HW side.

 

[longeggs]

It has an expansion vessel on the cylinder too, actually.. thats something at least

 

[longeggs]

I'm happy to convert to real fully pumped s-plan .. but the boiler has two flow/return pipes.. how do i terminate one of those safely?

 

[longeggs]

Like this maybe... ?

I can't find anything online or in the bluebird 90/120 manual about how to terminate one of the flow/return pipes.

 

[ericmark]

It would need a relay. Standard S plan the motorised valve acts as a relay for both pump and boiler, so one set of contacts, but you need the pump and boiler to run independent so it needs two sets of contacts so needs a relay.

 

[longeggs]

It would need a relay. Standard S plan the motorised valve acts as a relay for both pump and boiler, so one set of contacts, but you need the pump and boiler to run independent so it needs two sets of contacts so needs a relay.

Thanks. If I combine the two flow/returns from the boiler into one flow/return and I do a standard S-Plan, no relay needed right? The pump can run whenever the boiler fires for either CH or HW since it would be fully pumped... and no more gravity anything?

 

[ericmark]

Thanks. If I combine the two flow/returns from the boiler into one flow/return and I do a standard S-Plan, no relay needed right? The pump can run whenever the boiler fires for either CH or HW since it would be fully pumped... and no more gravity anything?

Yes, I am an electrician not a plumber, I was advised by my plumber, that the C or Y plan allows the boiler to cool by heating the DHW, and is so less strain on the boiler, so I still have a C Plan.

The summer DHW using the C plan was expensive to run, the only control I have is time, so summer I use an immersion heater for domestic hot water, so I don't select DHW on its own at any time, I just have CH control and the DHW heats at the same time.

 

[longeggs]

Yes, I am an electrician not a plumber, I was advised by my plumber, that the C or Y plan allows the boiler to cool by heating the DHW, and is so less strain on the boiler, so I still have a C Plan.

The summer DHW using the C plan was expensive to run, the only control I have is time, so summer I use an immersion heater for domestic hot water, so I don't select DHW on its own at any time, I just have CH control and the DHW heats at the same time.

Interesting thanks I didn’t know this.. c plan still on the cards then ! Can I be annoying and beg that you draw your setup or explain more please ? I’m so confused with how your pump works in a c plan .. it’s what I’ve been struggling with.. because your boiler must also have two flow/returns ? Where does the the pump sit? Do you have an unvented cylinder ?

 

[ericmark]

Your picture is basic, what I have, but I also heat two zones, the flat and main house, so need the zone valves, or I get reverse flow in the zone not in use. If I did not have the flat, then would not need zone valves. The controller was useless, as only two cores working on the three core cable main house to flat where the boiler is, and the thermostat for the flat (bottom) still used, but the receiver was there, but no actually thermostat up steps, in main house, and someone thought selecting pump would select area heated, that did not work, it just went back wards through the other zone, so I got the zone valves added. This plan had to me modified with relays added, but gives the basic wiring. To be able with hard wiring to control both CH and DHW I used Nest Gen 3, it did not work very well, as will not link to TRV heads, so now I have both Nest Gen 3 and Drayton Wiser thermostats, both in parallel for the main house. The Nest Gen 3 allows me to turn on the boiler for DHW in an emergency. But since the immersion heater changed from 9" to 27" never needed to use it. Not tried to draw a bath in summer, we use instant electric showers, but when we fitted solar panels we also fitted iboost+ so we could use excess solar. Really a mistake, but it does show how much energy used to heat the water with electric. This was an eye-opener, as I had always thought cheaper to heat DHW with gas or oil, but to heat with oil, needed to run the boiler ½ hour a day, well it only actually ran for around 20 minutes, so a 20 kW boiler, so for 28 days around 180 kWh, clearly we have losses in pipework, and the boiler which are far higher than I had thought, so even without solar or off-peak it is still cheaper to use electric in the summer.

Since we have off-peak at 8.5p/kWh and get paid 15p/kWh for export, the iboost+ would be better replaced with a simple time switch, and since we use electric for DHW in summer, the Nest Gen 3 is also redundant.

 

[longeggs]

Many thanks, that helps ! So no pump or valve on DHW either… is yours also an unvented cylinder ? I suspect what happened with my property was it was once upon a time a vented gravity cylinder.. then at some point an unvented tank got dropped in but they didn’t bother updating the boiler plumbing so kept the c plan .. which makes me uncomfortable

 

[fixitflav]

It's 100% unvented and 100% doesnt have the necessary safety controls.

Vented or unvented doesn't affect how the system is controlled on the primary side.

 

[fixitflav]

Like this maybe... ?

View attachment 395576

I can't find anything online or in the bluebird 90/120 manual about how to terminate one of the flow/return pipes.

Unless somebody corrects me, I believe both the flow (and return) pipes connect to a common space inside the boiler, so you can just blank one off and pipe to the other.