F23 on Vaillant ecofit pure 415 - lukewarm rads

29 Apr 2022
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United Kingdom
Hi all,

I'm puzzled by my CH and HW system. I appreciate any help you could give me.

I've got a gravity fed system with Vaillant Ecofit Pure 415 on heat only, a grundfos ups2 15-50/60, Fernox TF1 omega for crap catching and a Honeywell 3 port valve. British Gas charged the previous owners a lot of money for powerflush and new boiler etc 4 years ago. House is 1970s 3 bed end of terrace.

We moved in and radiators were getting progressively lukewarm at the top then boiler started throwing F23 at me. I keep turning off and on again for a few months until I found this forum.

Since then I've been confident enough to:
Drain down a couple times, add sentinel x400 for a week and flush after banging rads with rubber bat. take off actuator head and remove the ball in the valve giving it all a clean and inside the valve too. Ran water through Fernox filter often, looks pretty clean now. Manually, the ball moved freely so I replaced with a new tower actuator (as I'm skint). Cleaned out F+E tank which was minging .

I've balanced the rads and bled them loads (bled stalk at the top of system daily). I've not touched the HWC return valve.

Pump moves freely when I bled it and wiggled about with screwdriver. It vibrates a bit when in operation but not too loud.

Where I'm at now : on CH only mode with pump on 3, the hot water reaches the last radiator downstairs but the whole system doesn't get hot enough (upstairs nearly does). When on pump 2 (which it was when I moved in) the last rad downstairs doesn't get hot even if turn off the rad before it.

F23 occurs less often than before, however when someone takes a shower (which has pump in the airing cupboard) it always gives an f23 error.

Any ideas on what you think is knackered?

My next step is to get the grundfos pump off and give it a clean.

Many thanks for your time.

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Are any valves shut, eg ones that may be installed on the filter?
Are any valves shut, eg ones that may be installed on the filter?

Thanks for your reply. Not that I can see


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