It rather sounds as though you have a build up of sludge from what you say about the LLH. Has the system ever been power flushed? Toodles.

@toodles we had it done last year (the magnet one, rather than a power flush) but there does seem to be sludge around as there is still lots of bits and fillings in the small magnaclean filter. 

At the moment, we have a huge loss of heat between the LLH and the DHW and virtually a 100% loss between the LLH and the heating circuits. When the LLH was removed, it was better (got ~40c into the heating circuits) but the boiler wasn’t modulating then. 

@hubb84 The Magnaclean filter is for everyday removal of particles of any ferrous material circulating in your pipework; I doubt that even if you cleaned out the filter daily, you would ever be likely to achieve a fraction of the muck removal that a power flush would. I’m not trying to suggest that this is your ONLY problem but the fact that you found a lot of sludge in the LLH and the Magnaclean also picked up some particles seems to suggest their is muck in your system and it isn’t Yorkshire Brass!

Your pump would appear to be able to deliver the heat you want but as it is not flowing into the radiators properly (or the DHW tank) it rather suggests a very restricted flow. This may be muck, it may be valves that aren’t opening fully - both aspects are worth checking I think. Regards, Toodles.

@toodles ok thank you. I’ve booked a power flush for next week and see where it goes from there. I agree that there seems to be some sort of restriction, so it’s just trying to find what and where. 

will update next week! 

@hubb84 😏

@toodles 

ok so update from today: they tried to hook up a Magnaclean (the big one) on the return but we weren’t getting any, or very little, flow. This would explain why things take so long to warm up, or don’t get warm at all. 

We checked all pumps and one (on the downstairs radiator circuit) has failed. Whilst this makes sense for not having any flow on that circuit, I don’t understand why we had the same issue when turning this off and running the other circuits separately. 

Took two radiators off and both were quite full of stuff, but when we tried to flush the system just with the mains pressure, it was clear. 

They’re hesitant to do a power flush as we have a lot of plastic piping too…anyone have experience with this? 

At a bit of a loss now as to what to try/do next. 

@hubb84 No experience here I’m afraid, but I think your work has confirmed that you have sediment build up. If plastic piping isn’t up to a power flush, might there be a chemical approach? I have in mind using a solvent or sludge softening agent of some sort (if there is such a thing???) I would imagine the likes of Fernox would be the people to ask about such a solution.

Perhaps the pump that failed died of congestion? Are there any power flushing schemes that use suction rather than pressure? Sorry no solution but lots of questions from someone with very little knowledge of such a problem. Regards, Toodles.

@hubb84 Try looking at powerflushassociation.com. They may have a solution to your need to flush out plastic pipes. Regards, Toodles.