valiant turbomax hot water intermittent

[potnoodlecurry]

I have a vaillant turbomax boiler quite old probably 15 years old.

I had an engineer come round to clean the heat exchange because I've had problems with my hot water.

but I still have the same issue. best suspect it might either be the flow switch or some other issue.

they don't suspect it to be the heat exchanger because of the water that comes out is very hot. once it's hot and gets going the temperature remains very hot. when I turn the tap off and turn it on again there sometimes is a dip in temperature. when I turn the tap on on I don't get the signal that the boiler is firing up to heat the water up. it is intermittent and random. I can leave the hot water running for a long time over 5 minutes and no change in temperature. when I switch the tap off and on again I might get hot water. the radiators get hot with no issues there is not a problem with the radiators.

now if it's not the heat exchanger because it seems to have been cleaned quite thoroughly with acid, and because I'm getting a very high temperature as per usual I was told by the engineer that if it was a heat exchanger issue the water would come out lukewarm and wouldn't get hot as strongly as it does.

does anybody have any idea what the issue could be?

 

[muggles]

Sounds like you've done a better job of diagnosing this than the monkey who's sold you an unnecessary acid flush. From your description, I'd say that it's the flow sensor that's giving up - quite a common issue on these, but often mis-diagnosed. The sensor is a turbine which spins when a tap is turned on. The outer casing breaks up, causing the turbine to jam, thereby preventing the flow of water being sensed. I'd look at that first - it's a fairly cheap part

 

[Gasguru]

Turbomax..black panel and greeen knobs
Turbomax Pro or Plus..white panel

Which one is it.

 

[potnoodlecurry]

Valiant Turbomax VUW GB242/2-5 R3
Turbomax plus 824E

Light grey panel..

could someone please so kind enough to help me identify the part online so I can go and purchase it.

is it an entire flow switch, or sensor, im not sure what im supposed to buy?

many thanks

 

[Gasguru]

https://www.nationalboilerparts.co.uk/product/vaillant-flow-sensor-turbine-impeller-194829-194819/

or change the whole brass lump.