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Viessmann heating issues

Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls

Last Post by Toodles 2 years ago

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HUBB84

(@hubb84)

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Joined: 2 years ago

Posts: 4

Topic starter 20/04/2024 8:42 pm [#1506]

Hi all,

new to the forum and looking for some help please as I’m a bit at loss with my heating system.

In short, I run a 35KW Viessmann boiler that’s operates by a Vitotronic 200-H. The system has a LLH and 3 heating circuit pumps with mixer valves (one for underfloor heating, one for downstairs rads and one for upstairs rads), plus another pump for the hot water tank. Everything is weather compensated.

My issue is essentially that not enough heat is being drawn from the low loss header. The hot water tank takes around 2-3hrs (!!) to get to it’s desired 50c temp, and on the heating circuits, the flow temp never really gets above 40, even if the boiler is producing 75c+.

As an experiment we removed the LLH, which seemed to improve things, however the boiler was then constantly running at 75c (rather than running at reduced temps of ~50-60 due it’s weather compensation), whilst the radiators were still only getting up to ~40.

We’ve since re-installed the LLH which makes the boiler operate like it should (running at Lower temps), but now the mixer valves seem to be stuck on cold (it’s 8c outside) and having a flow temp. of no more than ~25. I’ve tried increasing the heating slope and curve and whilst this makes the boiler temps increase, the mixers refuse to move and flow temps are low. The LLH is boiling hot but no heat seems to be leaving this.

Any ideas? Could the LLH have failed (there was a lot of rust in it when we cleaned it out)? Could there be sludge/build up in the system causing this?

Any ideas/suggestions would be very welcome!

thanks in advance!

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Toodles

(@toodles)

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Joined: 4 years ago

Posts: 2694

21/04/2024 4:03 pm

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, heats his home with cold draughts and cooks food with magnets.

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HUBB84

(@hubb84)

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Joined: 2 years ago

Posts: 4

Topic starter 22/04/2024 7:25 am

@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.

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Toodles

(@toodles)

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22/04/2024 2:19 pm

@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, heats his home with cold draughts and cooks food with magnets.

👍

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HUBB84

(@hubb84)

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Topic starter 23/04/2024 9:02 am

@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!

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Toodles

(@toodles)

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23/04/2024 9:09 am

@hubb84 😏

Toodles, heats his home with cold draughts and cooks food with magnets.

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HUBB84

(@hubb84)

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Topic starter 29/04/2024 5:02 pm

@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.

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Toodles

(@toodles)

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29/04/2024 5:32 pm

@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.

Toodles, heats his home with cold draughts and cooks food with magnets.

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Toodles

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