Vaillant boiler hot water problem

[tman247]

Really looking for some quick advice if possible. We have a Vaillant Ecotec Pro 28 R2 combi boiler, installed in late 2010. Model number is VUW GB 286/3-3. The boiler has generally been ok, and is regularly serviced.

A few weeks ago, we started having a problem with the hot water. It would get hot (burner would light), and the water temp would climb to ~70deg, then after a 20-30s the burner would go out and the water temp would drop to around 40 or less. This was especially noticable when having a shower as you can imagine! If you turn the hot water off for 30s or so, then back on, it would repeat the same process. Now, we've also started getting an F.23 error on the boiler.

After discussions with the engineer, we've replaced the plate heat exchanger, heat exchanger thermistor and both the NTC flow/return temp sensors. but it hasn't fixed the problem. I know the boiler is getting older and will need replacing at some point, but I know there's a fix for this - I just need some guidance if possible. Strangely, the radiators have no problem - they get hot and stay hot, and when the radiators are on, the water seems to stay hotter for a bit longer.

Thanks a lot

 

[ianmcd]

switch the heating off and let it cool down, then run a hw tap and hold both heating flow and return pipes below the boiler and see if one heats up when only hw demanded

 

[tman247]

Thanks for the reply. I've tried this with the heating off. The return is warm to the touch, and stays warm when I turn the hot tap on. The burner lit for about 10s, and the water temp increases, and the flow pipe gets hot for maybe the same amount of time, then the burner goes out and water temp falls back and the pipe cools down rapidly.

 

[ianmcd]

Sounds like you have a diverter valve problem

 

[tman247]

Thanks. Diverter valve was replaced a few months back with a brand new one (it was leaking), and we never had the problem then. I'm going to bleed the pump and bleed/clean the Magnaclean if I can. Not sure what else to try. One problem we've had with this boiler is the PCB. We're on our third one now - they seem fragile, and the relays are prone to failing. Not sure if that could be part of the problem or not.

 

[CBW]

Not sure if that could be part of the problem or not.

I Highly doubt it. I’d get the canoe filter checked.

 

[tman247]

Not quite the result I wanted, but had to sign up to a 6 month Vaillant care plan in the end to get a Vaillant engineer out. When he arrived, he said he would have inspected/changed everything we'd already tried anyway. He checked/cleaned the canoe filter and was putting it back together, when the magnaclean literally fell off in his hands (broken thread). Vaillant agreed to replace this part (not normal), so had no heating/hot water at all for the rest of the day until he could come back the next day (which he did @ 8am). One new magnaclean later and the boiler started working normally again - the flow/return temps wen't straight back to normal, so no more F.23 errors, and hot water is working properly again. I guess we get 6 months cover to think about how we're going to proceed too, but it was probably just gunk in the system. Still cost me best part of £500 to get it fixed with the parts/plumber costs and care plan!

 

[ianmcd]

well you should have got the care plan in the first place instead of just throwing parts at it

 

[dilalio]

Can't see how the magna leak would affect the DHW!
But then again, I've had a skin full!