it's not so easy to see which pipes go where, and it's kinda tight for taking a decent pic, so i've marked up the pipes as best as i can below



red - from boiler
blue - return to boiler
purple - to radiators
yellow - 15mm from header tank
white - vent pipe

the vent tees off the pipe from the boiler under the floor
the fill from the tank joins the same pipe just in front of the pump

new years eve 2019 the pump failed, and nowhere was open who had a matching pump (standard old grundfos thing) so it was swapped for this posh one that maintains constant pressure, speeding up or slowing down as the TRVs open and close.

I don't know if it's relevant or not, but when the cylinder was changed about 10 years ago, the pipework coming from the syslinder was slightly modified.  originally the blue pipe coming from the cylinder was reduced down to 15mm for about 8 inches, then back to 22.  i had to cut the pipes to get the cylinder out, and it was replaced with 22 as that's all I had

don't know if it's related, but when the boiler is on doing hot water only, the landing and bathroom radiators get slightly warm, but the water is flowing the wrong way (lockshield end gets warm first, not the TRV end as it does when the heating is on.

At some point in the near future, the whole lot will be being ripped out again, as i want to fit a solar hot water system as well, so will need to put a twin coil cylinder in

I think that there may be more than 1 return connection for the rads which is causing the back flow when its on hot water only, but that will be under the floor somewhere

Fill is closest to the pump, probably about 3 inches from it.  The vent is gonna be another 8 inch past that at a guess.  

Pump is a grundfos ups3 15-50/65 130

The valve (tower mid position valve) is getting tired and makes some odd noises when it switches on

https://youtu.be/jTiJsEHCQnU

First putting it on heating only, then the screaming noise is it going to hot water only

If its not a daft question, why isn't the fill and vent done as 1 pipe?

Filling ours is a pain anyway.  I can still hear air moving about somewhere after a week

There is an air vent pipe on the pump side of the cylinder.  Its the pipe you can see sticking up in the first pic, with the compression fitting on it.  

We were having problems with air getting in to the system, so I extended the pipe with the vent on, so it would be able to collect more air and not need bleeding every single day.  It has since been traved and sorted (pin holes in a rad, replaced rad and it stopped) so could really be shortened again.  I just haven't got round to it

I should have called that an air bleed, not an air vent.  Sorry!  The air in the system problem went away after replacing a couple of pinholed rads and replacing some elderly TRVs

I'll try the glass under the vent next weekend.  Won't have time before I'm back to work later today

when the heating was installed, her ex-husband did it on the cheap.  there was a handful of rads that were 2nd hand as they were "the right price" (presumably free)  i've replaced 8 out of the 11 rads over the last few years as i've been decorating.  i hate brush painted rads, so the ones that were looking scruffy just got changed.  they're cheap enough that i don't think it's worth the hassle of removing them to spray them.  

and yes, one i had run the cleaner through and flushed the system out a few times, it did get refilled with 2 bottles of F1 in it

I get whatever the closest size is in their clearance range.  The landing radiator got replaced with a 500x1800 single panel which cost me £18. For that money I wasn't worried about modifying the pipework a bit

Yes thanks