I was wrong, Octopus did put a strainer/filter on the return correctly as well as the flow out to the heating system.
I hadn’t appreciated there might be two, and the second on the return looked like a standard isolation valve.
Unfortunately it was jam packed with debris - literally so bad whilst still in the valve, I couldn’t get a finger in and had to dislodge the sediment which promptly fell onto the floor. No idea how it was still working.
I then pulled out the strainer/filter on the return, and this is what was left:
Up to a max of ~34L/m now - that’s up ~10L/m (~40%) from yesterday after cleaning out both strainers/filters (the other way of looking at it, it was down to ~70% of a near clean system at my house):
My system clearly needed flushing, and still does.
Until then I’ll keep cleaning these both out and keep an eye on flow rates which if monitored over time, can show how healthy things are.
I will update/edit my post above to reflect the other strainer/filter.
Worth checking!
I see that @Zarch noted this (and strangely the exact same % drop in flow rate!) on his annual service a couple months back, so really is a thing and I guess maybe more focus placed on relative flow rates vs new/clean system, as it could be impactful and very very easy to clean out.
https://twitter.com/Zarch1972/status/1701963948147286116
Servicing works!! Don't scrimp on this!!
— Mick Wall (@Zarch1972) September 13, 2023
I never realised the role the strainer played in the whole system.
DHW run before cleaning: 840 litres/hour
DHW run after cleaning: 1190 litres/hour
And there wasn't a great amount of crap in there really.#checkyourstrainers… pic.twitter.com/YyT4KP74rP