@jennyross out of interest did you get an RHI grant? Was your existing system flushed and cleaned out originally? Because building regs Part L, page 56 says "8.8 Before a new heating appliance is installed, all central heating and primary hot water circuits should be thoroughly cleaned and flushed out." It then goes on to detail treatment with inhibitor. 

Have you seen the colour of the water yourself or were they just telling you about it?

Personally, IF your original installer makes good on their job, I'd at that point ask Vaillant for another recommended maintenance engineer as what has happened, and what you are relaying has been said to you, doesn't sit right with me. I help to run a renewable heating distribution company and if this was one where we'd supplied the kit then I'd be concerned. 

@toodles Thank you 🙂

@jamespa Thank you - we'll reflect on these things and make a decision about how to play it.

@sune they did include a soak away

@sune yes we did get an RHI grant (£7.5k for the ASHP and £2.5k RHI)

I can only say that I assume that the original system was flushed out and cleaned out originally. I haven't seen the colour of the water but I have seen one of the small filters clogged with black gunge. The radiator pipes were running clear. It is the HW tank that is problematic. Everything was brand new in 2021, including the HW tank.

I did consider asking Vaillant to visit. Whilst I have my own installer blaming another company for poor service carried out in 2023 (in his view) and that he now has to rectify the problems of others - I feel concerned about inviting anyone else into the picture at present. As you say - once the problem has been sorted it might be worth getting them down here. 

The company that serviced the pump in 2023 performed the list of tasks attached here. I'm not sure if you can read this. My installer serviced it in 2022 but gave me no list of tasks and was predictably silent about what he had actually done - my feeling is that he wants to continue to mystify the whole process so that he stays in a job.

Posted by: @sune

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Because building regs Part L, page 56 says "8.8 Before a new heating appliance is installed, all central heating and primary hot water circuits should be thoroughly cleaned and flushed out."

This is the first time I’ve heard this. Super interesting. Thanks @sune. Our system was emptied and refilled, but not flushed. I’m guessing this is very often the case. 

@jennyross where are you based roughly. I’ll raise your case with Vaillant and see what they say, but I’d also escalate the matter if I were you.

@editor Thank you Mars. I’m based in NE Fife, near Cupar - about 10 miles from St Andrews. 

@jennyross it's helpful to have a list isn't it! Cleaning filters should be on that list - it's probably one of the most vital parts really (as well as any magnetic filters you may also have a Y-strainer filter on the return pipe near the heat pump), and checking the dosing of any water treatment. Running through basic control settings would also seem sensible.

@sune yes it seems extraordinary that cleaning filters wasn’t on the list and I missed it at the time. Somehow a list seems reassuring but not if you don’t read it 🙄 I trust too much and expect ‘experts’ to know what they are doing.
I meant to say that the black gunge from the HW tank was less biological in appearance (stuff that accumulates at plug holes and the overflows in sinks for example) and more physical gritty black stuff blocking the filter. (Apologies for such technical descriptions. )

@sune when we emptied our system, I don’t think we had any glycol because it was an oil boiler that was previously running. I guess the extra headache of draining a system (and flushing it) that has glycol in it is its safe disposal, especially if it’s ethylene glycol.

@jennyross Were you to put a magnet to the sludge, you will soon know if it is of a ferrous nature rather than biological. Regards, Toodles.