Vaillent possible NTC fault

[doov75]

I have a Vaillent Turbomax plus 824e combi which has developed a fault that I could do with a second opinion on.

We have always controlled the heating with the manual time clock but recently the boiler has been coming on with no demand. I complete my ACS and Gas Safe registration at the end of the month, so while I have a certain amount of knowlage I still concider myself an apprentice. I assumed that it was the time clock as when the boiler was set to constant it worked fine. I replaced the clock but the fault persisted. Having followed the fault finding section of the manual, the diagnosis was the PCB, which I've changed. Fault persists. Then I cleverly looked at the most recent fault codes (told you I'm an apprentice) and that tells me that it is the flow NTC. The first code was F.00, and the second was F64. Can't find out what 64 is as the manual tells me F.60/67 mean irreversible electronic system malfunction.

Can anyone help with the following.

What are the symptons of the flow NTC failing?

How can you test if it is the cable or the probe?

The boiler comes on and off at random and in bursts but temperature is controllable. Is there anything else that might be causing this?

Cheers

 

[Gas2Air]

ACS and Gas Safe? Get you.

Do you have a multi-meter? Test NTC cold for resistance, the colder the higher reading. Leads off. With leads test for continuity.

Very expensive fault finding so far doov. Who do you work for?

 

[The831Bunny]

Firstly turn OFF the 'Warmstart' (pre-heat) on the Dhw knob. Turn it all the way to minimum till the green LED goes out. Then back to about two thirds of the way round. This should stop the heating coming on when the clock is off. The root cause is likely to be a sticking diverter valve. You can also try running the hot water and feeling the heating flow pipe. It should remain the same temperature and not get hotter. If it does, it confirms the DV is faulty. Its like Russian roulette so you may have to try quite a few times to catch it doing it.

Have you seen F.00 or F.64 on the display accompanied by a red LED? these are codes that need resetting. More than likely they were in your fault history previously and transferred to the new PCB.

 

[doov75]

Ain't that the truth. Work on a maintenance crew, so the expencive fault finding has yet to be beaten out of me.
Will get a multimeter from work and do some investigating.
Cheers

 

[doov75]

831 bunny. Cheers mate.

 

[The831Bunny]

831 bunny. Cheers mate.

No probs. If you're new here, the done thing if you are happy is to click the 'thanks' button on the post

 

[Gasguru]

Top tip for you.....

Don't waste your time with fault finding charts, they rarely have the actual faults on them, the yes/no options can be reversed, they'll lead you to swap half the boiler parts...most pros never look at them.

Next top tip......

Fault codes are a guide and very often wrong too!

Join the combustion chamber once you've passed and then you'll start to learn...ACS has nothing to do with repairs.

As previously mentioned the issue is likely top be the diverter...unhook the motor head and check the pin is free to move using long nosed pliers.

 

[doov75]

Well its not the diverter valve. The pin moves up and down when tried, it does feel as if it is passing through Diaphram of some sort but it seems free to more.

 

[Gas2Air]

Well its not the diverter valve. The pin moves up and down when tried, it does feel as if it is passing through Diaphram of some sort but it seems free to more.

Well if nothing else, you're getting experience

 

[Bunnyman]

Well if it's a plus it has no diaphram ? That's only on the older turbo, as 831 said it more than likely the diverter it's a known fault with the symptoms you describe. As he said turn the warmstart off fit that stops it then it's the div. also if you have had the motor off on the div make sure you hook the ball end back on or you will have problems