Advice on hybrid configuration - vented heating with unvented hot water

[JohnB-2233]

Hello everyone,

Please can I have your advice on this hybrid configuration that involves vented heating & unvented 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 unvented 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.

 

[Scott_D]

Sounds fine to me.
Is there a reason you dont want to seal the heating system

 

[SJB060685]

Absolutely no reason why the heating system has to be pressurised. Still holds the same volume of water but a sealed system is usually at a slightly higher pressure. The advantage of a sealed system would be to completely free up the loft space and have every serviceable part within, or close to the boiler.

 

[JohnB-2233]

Sounds fine to me.
Is there a reason you dont want to seal the heating system

My thinking is there is less risk with regards to leaks i.e. no need to worry about leaks on the heating side (by not going high pressure), I only have to worry about potential leaks (due to the pressure increase) on the hot and cold water piping. Also i wont have to recharge the heating side of things, as the F&E tank will take care of that.

ps. I was advised to move away from a Y to an S configuration (ease of troubleshooting) and ensure an auto bypass value was put in place.

 

[SJB060685]

My thinking is there is less risk with regards to leaks i.e. no need to worry about leaks on the heating side (by not going high pressure), I only have to worry about potential leaks (due to the pressure increase) on the hot and cold water piping. Also i wont have to recharge the heating side of things, as the F&E tank will take care of that.

ps. I was advised to move away from a Y to an S configuration and ensure a auto bypass value was put in place.

The problem with open vented systems is if there's a leak it will constantly refill the system, whereas a sealed system will not. If a leak sprung while you're away for a week the damage done on an open vented system will be large, not the case with a sealed system. If you want to stay open vented that's your choice and any engineer should know that still, even today open vented works no different to sealed.
I never liked Y plans, they are a complicated valve that can cause a host of problems and they are not suitable for unvented cylinders, unless an additional 2 port is installed on HW flow after the 3 port and some additional wiring. I can supply an image of such but anyone installing unvented cylinders should be aware of this and know what to do.

 

[JohnB-2233]

thx for everyone's responses, much appreciated !

 

[gmartine]

Pressurising the heating circuit also makes it more efficient (less heat loss) as well as not allowing any oxygen ingress which causes corrosion, and allowing you to get rid of the F/E tank. Debris cannot enter the system and if there is any pressure loss caused by a leak or trapped air you'll know about it.

 

[Timmy D]

My thinking is there is less risk with regards to leaks i.e. no need to worry about leaks on the heating side (by not going high pressure), I only have to worry about potential leaks (due to the pressure increase) on the hot and cold water piping. Also i wont have to recharge the heating side of things, as the F&E tank will take care of that.

ps. I was advised to move away from a Y to an S configuration (ease of troubleshooting) and ensure an auto bypass value was put in place.

S plan (2 port zone valves) are required for unvented cylinders as they are a safety device.