AquaPLUS hot cold hot cold

[simond]

We have a Vaillant aquaPLUS in the family (mother in law) that intermittently plays up.

Bit embarrassing because whenever we go round it works perfectly, so it is really difficult to diagnose.

Problem is that when running HW it sometimes goes cold for a while. Apparently the tap symbol remains lit. The heat exchanger is clean.

We have changed the diverter valve this week, and mother in law said it was better. Next day she rings to tell me it is back to its old tricks.

I don't want to change a load of parts unnecessarily; Vaillant have advised changing the NTC but in my experience these are not intermittent, the resistance is either within limits or it isn't.

I was wondering whether other Vaillant experienced types Eg: dangermouse or Dave had any suggestions. Did wonder about the fan switch but no error code is logged.

Any ideas?

 

[gas4you]

Simon, I have no direct experience of this Vaillant, but generally I have found of late that ntc's can be intermittent (to my detriment ), even when they read the correct resistance cold etc, so can only advise going along with Vaillant tech's suggestion.

As you have changed the DV, a ntc is a very small and cheap 'experiment'

 

[Deleted member 105431]

when it plays up press the i button and look for s33-this is a fan/venturi/aps fault (black aps' are dodgy the white/grey are good) that can be very intermittent on this model (particuarly the plastic venturi warping/melting). If the plate is clean as you say it may be worth checking the dhw circulator pump motor is working.


btw these faults won't always trigger a F code so s33 in the status menu is the only certain way to "catch" it.

 

[simond]

Thank you very much for the prompt response, chaps, I appreciate it. Will follow your suggestions up.