Central heating layout. This should work, right?

[GreyBana]

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!

Before I finally commit, I just had a couple more questions if you kind folk would be so kind to share your expertise on. The below is a portion of how I'm intending on reconnecting up C/H system. The vent and feed (apologies for my likely butchering of terminology) are in the same logical place as it was before I began the renovation, but the actual runs of pipe are different. I wanted to check that I won't have any problems with this, as I've read that the pump can sometimes pull air down the vent pipe and into the system; it didn't seem to happen before (or at least I didn't notice if it did), so I'm assuming this is still an acceptable way to plumb it? I've read about tying the vent and feed pipes together, but the specifics of the 150mm rule aren't clear to me, or whether I actually should tie them together at all?

The only other question I have is around the specific levels/measurements I need to adhere to around the crook at the top of the vent pipe?
Other than that, any other general comments are always appreciated!

Thanks

 

[ericmark]

Even if you had all the heads marked, it's not a simple yes or no, in real terms suck it and see. Even the direction of filler pipe can make a difference.

 

[denso13]

but the specifics of the 150mm rule aren't clear to me

Better sticking to this, the rest is fairly simple.

 

[GreyBana]

Even if you had all the heads marked, it's not a simple yes or no, in real terms suck it and see. Even the direction of filler pipe can make a difference.

Thanks @ericmark, as long as it's not clearly wrong then "suck it and see" works for me.

Thanks @denso13, that's a great resource you've linked! Given the layout I've drawn out above, horizontally the vent and feed pipes I have are about 330mm apart, which doesn't sound ideal... As I have the vent on the flow and the feed on the return, while they are about 330mm apart horizontally, they are probably a metre or two apart once you take into account the height difference and internal geometry of the boiler. Which is the relevant distance, 150mm through the pipes, between where they T off, or strictly horizontally? It's not intuitive to me what the 150mm rule achieves, something something pressure difference?

 

[denso13]

150mm through the pipes, between where they T off, or strictly horizontally?

150mm max horizontally, both on the flow.

something something pressure difference?

Yes, just that. Prevents pumping over the expansion and stops drawing fresh water in.

 

[GreyBana]

So this is a picture of what I actually have (annotated), hopefully you can see how that marries up to the diagram in my original post:

I don't see how it would be possible for me to get the vent and feed closer than 150mm when the pump itself (plus valves) is 330mm wide?

 

[denso13]

it would need some re-piping. It isn't just the distance though, they should both be on the flow, before the pump. With the feed and return separated of course.

 

[GreyBana]

Ah, I misunderstood the image you attached earlier. This makes more sense now, thank you for explaining. For some reason I thought the vent needed to be before the pump and the feed after.

It looks like I only have enough room to shuffle the pump over by about half the distance that I need for an end feed 22mm to 15mm Tee. Any thoughts on how I can get a 15mm pipe down to the right place, something like this maybe (blue line being a 15mm feed)?

It otherwise look like a much bigger job

Thanks agian for your help on this!

 

[denso13]

Should really be on the flow, not into the vent. The other bit of bad(ish) news is that the pump shaft should be horizontal, not at an angle. Sorry, you did ask.....

 

[GreyBana]

Thought you might say that lol. I'll have to see what I can shuffle around tomorrow I think.
Thanks for pointing the pump angle out, always better to know than be oblivious to it.

 

[denso13]

Maybe raise the pump up a bit to clear the cylinder, give you more room.

 

[GreyBana]

Yeah, perhaps that's the way I'll have to do it. I was trying to be as space efficient as possible, but that's bitten me in the ass ha.

Just looking at my options here...

Combined cold feed and vent | UK Plumbers Forums: International Plumbing Advice | Plumbing and Gas Engineer Forums

Combined cold feed and vent, UK Plumbers Forum and UK Plumbers Forums: International Plumbing Advice | Plumbing and Gas Engineer Forums.

ukplumbersforums.co.uk

These guys are discussing a single, combined 22mm feed/vent pipe. This would solve my problems, but with no experience behind me, I can't really evaluate whether this is a good idea or not?

 

[denso13]

I've only done one or two of those, and it was a last resort to solve other problems. Can be a pig to fill the system as you are filling and venting through one pipe.

 

[GreyBana]

Mm, yeah, makes sense it would be tricky to fill. I've also got it at the back of my mind that in a few years, this boiler from '94 is probably going to die and I'll be going for a combi boiler with a pressurised system and pulling a bunch of this out.

Bah, I don't know, I feel like my options are:
- Leave it as it is (in the first diagram and image) and hope it'll be alright (that is how it was installed to start with...)
- Move things about as you've suggested (but that is feeling like it could end up being a lot of work )
- Have a combined, 22mm vent and feed pipe.
- Ditch the old boiler and pressurise the whole thing (££££, would like to run this boiler until it dies if I can really...)

Any words of wisdom? How would you rank those options?

 

[denso13]

Probably go with the first one. It could be ok but I think it's only right that we explain how things should be done.