Central heating layout. This should work, right?

[GreyBana]

Thanks, I really appreciate the advice and pragmatism. I absolutely agree about explaining the correct way to do things and I'll definitely give it a good go trying to move it about within the constraints I have! If it does start looking like I'll have to moving things around on a larger scale, I'll leave it as it is and sort it out when the boiler inevitably pops.

Honestly, thanks for taking the time to go through this with me, it's been really helpful!

 

[Mister Banks]

Any reason why you are repiping as an s-plan system rather than PDHW. With all the work you are doing now seems like a good time to replace the boiler with a pressurised system boiler that supports PDHW.

 

[fixitflav]

Another day another question. Thanks for all the advice I've received so far from everyone. This weekend is going to be my big plumb up; think I have everything in place to get started now!

Cold feed on the boiler return is the old way, up till about 1970. Trouble with it is it causes seewsawing between the fill and vent on pump start/stop, drawing water with dissolved air into the system, and corrosion risk.
Edit - and if you're re-routing pipework, don't forget the rads returns must be commoned before the HW cylinder return comes in.

 

[GreyBana]

seems like a good time to replace the boiler

Yeah, that was definitely an option. Hard to weigh up the cost of a new one vs efficiency gains though. The hot water tank was in a different location in the property, but I've moved it, so it's next to the boiler, which will hopefully help when it does come to replacing the boiler. I think the main bit of lost effort will be in connecting up the header tanks, but I don't think that's too bad. I also don't have mains gas where I am, so when it does come to getting a new boiler, I'll have to decide on whether to stick with oil, or swap my tank out for a gas one (or pay the ~£60k (nope) to get a line run to my property)...

a pressurised system boiler that supports PDHW

I hadn't heard of PDHW to be honest, so will definitely look into it when the time comes. I had just assumed that I'd be looking at a combi boiler really; I like the idea of no hot water tank!!

Cold feed on the boiler return is the old way, up till about 1970. Trouble with it is it causes seewsawing between the fill and vent on pump start/stop

That is interesting, the property was built mid 90s and the boiler was made in '94, so not sure why they did it this way then...

I've been trying to move things about today as per denso13's advice, but it's looking like it's going to have a lot of knock on effects that I'd rather not contend with, which is really annoying. I think I'm going to leave it as it is and if I end up with problems, I'll try a combined 22mm vent and feed. Hopefully I don't get problems though, as this was how it was connected up before I moved things around, but who knows, pipes have moved around, so maybe that'll change things...

 

[Exedon]

I would strongly advise against a combined vent/feed .
I used to see them on a regular basis (heating team in this area were very fond of them) odd ones can be OK but I've regularly found systems to be absolutely filthy.
Plus as already mentioned combined vent/feed systems are notorious slow & difficult to fill.

 

[GreyBana]

Thanks for your input Exedon. I'm really hoping this first option will work alright and I won't have to revisit it. I'll weight denso13's layout suggestion higher if it comes to it!

 

[Exedon]

Probably not what you want to hear but I would seriously consider converting to sealed system.
Simpler pipework no open vent or feed tank.
With existing boilers we generally run system at 0.2 bar above system head.