Advice on hybrid configuration - vented heating with unvented hot water

[JohnB-2233]

Hello everyone,

Please can I have your advice on the following hybrid configuration that involves vented heating & un-vented hot water ?

I currently have a regular boiler (Worcester Greenstar 24 RI) running in a vented system, with cold water storage tank in the loft and also an heating F&E tank in the loft, pumped into a Y configuration that uses an indirect vented hot water cylinder.

The goal is to get rid of the cold water storage tank in the middle of the loft.

My suggestion to my plumber, to do this as cost effectively & efficiently as possible, is to keep the heating side as-is, i.e. keep the existing regular boiler; pump; heating F&E tank; Y configuration etc. but replace the existing vented indirect hot water cylinder with an un-vented indirect cylinder (Tribune HE) on the hot water side, with all the safety bits that go with this.

I'm happy to accept the risk of higher pressure on the hot & cold water copper piping, but see no reason why the heating has to also be pressurised as well.

 

[Gasguru]

Your plan is fine...however, to make the wiring very simple (and much much easy to diagnose faults) you should bin the mid position valve and buy a single 2 port zone valve and convert to S plan.
The cylinder will be supplied with a 2 port valve for the hot water circuit.
You would also need an auto bypass valve fitted after the pump but before the valves.
Do not go down the route of keeping the Y plan and adding the cylinder 2 port....it will cost you far more in extra diagnostic time when you get future problems with the valves.
I guess you've checked sufficient pressure/flowrates.

 

[bernardgreen]

but see no reason why the heating has to also be pressurised as well.

The reason is to "prove" to the boiler that there is water in the system. In a vented system the feed tank will replace any water lost from the heating system so except for a catastrophic leak there will always be water in the heating system.

 

[fixitflav]

The reason is to "prove" to the boiler that there is water in the system. In a vented system the feed tank will replace any water lost from the heating system so except for a catastrophic leak there will always be water in the heating system.

I don't think that's the question. He's not asking why it has to be pressurised, if a pressurised system is in place. He's asking does he need to go to a pressurised primary circuit if he changes to a mains-pressure HW cylinder. To which the answer is no, he doesn't, as gasguru has said.

 

[muggles]

The reason is to "prove" to the boiler that there is water in the system. In a vented system the feed tank will replace any water lost from the heating system so except for a catastrophic leak there will always be water in the heating system.

Worshitter RIs don't have any kind of sensor to tell them whether they're full of water or not. They'll quote happily fire away with no water in them at all, albeit not for very long

 

[JohnB-2233]

Worshitter RIs don't have any kind of sensor to tell them whether they're full of water or not. They'll quote happily fire away with no water in them at all, albeit not for very long

Not sure what other boilers have in terms of sensors to work out if the primary circuit is full of water or not, but i do know the Worcester Greenstar RI series does have a flow temperature sensor (NTC) and an overheating thermostat on the heat exchanger.

 

[JohnB-2233]

thx for everyone's responses, much appreciated !