Turbomax Plus 824E - DHW running hot and cold intermittently

[forwise]

Hi all,

I've run through quite a few similar threads but couldn't find an answer (or at least I'm not aware they were related).


I have a problem with my Vaillant TurboMax Plus 824E combi boiler.
Until very recently it was working fine with both underfloor heating and DHW.

Since last week it started developing a noise at the end of heating cycle for DHW (not the case for UFH). It sounds like small starting aircraft (Cessna). At the same time DHW started flowing from tap in cycles (hot-cold-hot-cold...). Boiler itself seems to be firing fine, no codes on display and temperature gauge is going from 60-82 C deg, then down and up again (as it was usually). Although hot water after measuring from the tap (located 1m from the boiler is flowing at 45-20-45 C and so on.

Does anyone have any idea what might be causing this?

PS FYI. I have water underfloor heating system consisting of 5 zones with it's own separate pump. Unfortunately I've noticed recently that the pump has started corroding internally and pipes got orange rather than clear. UFH works on demand with actuators at 50C demand temperature. So far no problems with the heating systems. I'm planning changing the pump and cleaning the pipes start of next year but need to get DHW sorted urgently.

 

[Nero]

Sounds like the calorifier could be blocked

 

[forwise]

Sounds like the calorifier could be blocked

Sorry, I'm newbie. What a calorifier is?

 

[forwise]

I had an engineer looking at it and the suggestion is that Heat Exchanger may be blocked. Looks like it's about £100 for parts and another that to change it. How likely is it that this may be the root cause?

Engineer didn't seem to be particularly confident about the guess/opinion and did not agree for fixed price. Shall call someone else?

 

[easyflow]

Not much of an engineer if hes not confident.
Run a hot water tap, if the flow and return pipes get warm, the diverter valve is suspect, if the flow and return pipes stay cool its most likely the plate heat exchanger.
Remove the hex and a good pointer will be its full of crud, get it descaled or replace.

 

[forwise]

Thanks.

The return DHW pipe is definitely not hot. Definitely not in comparison to Heating return pipe which is set to much lower temperature (55 C deg). DHW is set to 82 C deg and I can hold the pipe with no problems, it is just about pleasantly warm.

I've ordered new Heat Exchanger which should arrive today. Will give it a go but need to find the best tools for the job first (which is always a nightmare for me when DIY'ing).

 

[J_N30]

Chances are your new plate will block up in a matter of months as your current one has. The problem is a mucky system and it'll need cleaning out. Fitting good parts to a bad system is only going to bide you time, not solve the long term problem.

 

[forwise]

Ok. Both sound like good suggestions. Any ideas how I could clean the boiler installation?

Either instructions how to do it myself (DIY) or any suggestions about professional service prices would be great.

 

[forwise]

OK. Had to fiddle with the new Heat Exchanger but definitely it sorted out the problem. All that is needed to change it is:
- monkey wrench
- new HE (it should come with one seal + 3 clips to lock pipes)
- and quite a bit of patience

When connecting the pipes make sure that the thread isn't visible on the HE before putting clips on. It isn't easy to push it in (especially the one next to the pump) so start to go with them one by one and make sure they visually look clean. Tighten the cap for lower left pipe last.

Thanks for your help guys and gals.