'Upgrading' back boiler to C Plan

[scrabble1]

Hi all, I've recently moved into a house that has a Thorn Housewarmer 30/45 back boiler. Gravity HW and pumped CH.

Currently, the HW comes on with the heating and I would like to be able to control them independently. I have an electric shower and no need for a cylinder full of hot water. My understanding is that changing to C Plan by fitting a 2-port valve and cylinder stat would allow me to do this.

I've already flushed out the rads and fitted TRVs to most (except hallway where the thermostat lives, and bathroom) and have a Nest thermostat fitted, wired so that the HW comes on with the heating as per the old Randall programmer it replaced.

I'm not overly familiar with back boilers so just wanted to be sure of the basics - would I have any issues in replicating the following? Where does the heat in the HW circuit go when the valve is closed?

(Does it mean that the boiler fires up for less time when there is a CH demand as energy isn't lost to heating up the HW...?)

Valve and cylinder stat aside, that's a pretty accurate representation of the system I already have in terms of how it's piped up. Is there a better way of achieving what I'm looking to do that doesn't involve a great deal of upheaval? Not looking to change the boiler but instead do the best with what I have.

Thanks in advance

 

[CBW]

It wouldn’t meet current building regulations. You could upgrade to a modern S plan or Y plan and just not have hot water on for long?

 

[DP]

Fitting a motorised valve where you indicate will be accurate as per C plan but this valve will need to be 28mm or 22mm with head replaced (6 wires- end of travel switch needs to have orange, grey and white wires). A relay would suffice too if standard 22mm MV used.

Just fitting cylinder stat will allow hot water temperature control during summer and also enable use of controller in winter ( as no interlink to fire boiler when ch selected). Can do drawing for this option

Keeping present system, upgrading controls to higher lever, you will have an old system that is bombproof built likea brick outhouse, no current boiler has facilities that you will have.

 

[JackK]

I think I have a similar system - Ideal Mexico 2 boiler in garden which works without any servicing at all and a 2 port valve on the hot water cylinder flor which is tee'd off a pumped flow from boiler

I always have had to use the programmer to switch on the boiler in morning and evening to guarantee hot water and I got annoyed that the radiators also heat up at the same time.

Was thinking of removing the boiler and replacing with intergas hre OV.

I have a cylinder thermostat and a 2 port honeywell valve but the boiler only fires up when heating is called for - Asking for hot water has no effect.

Is this a simple boiler control problem or something else?

How can I have hot water without central heating coming on given there is only one 2 port valve -

 

[JackK]

What happens when the 2 port valve closes and hot water has been met? The boiler should really shut off in that scenario - But the way its been wired means that does not happen and its only central heating that causes boiler to fire

Is a wireless hot water cylinder themrmostat going to fix that ?