Eco Tec 824 hot water mystery

[Abcplumb]

Hi guys

Need some help pls.

The above boiler has a hot water issue, ch working perfectly fine.
When you turn the dhw tap on the hot water works fine for about 5mins then it suddenly starts to drop.
I had the dial set to 57c, the hot would come on and go to around 70c then drop to around 55 then back to 70 again, this continues for a few mins then it slowly decreases to 38 and it stays there. Until the tap is turned off and back on again.

I suspected the dhw plate, so I removed it but that was really clean.
The boiler is only 5 years old and has a magnaclean fitted.
Replaced a new pcb, but same issue.

Any ideas would be appreciated pls.

 

[Gas2Air]

Did you test the NTC before replacing the PCB?

 

[Abcplumb]

Did you test the NTC before replacing the PCB?

Nope, I thought if it was a NTC fault I would have got a fault code.
I'll be going back there tomorrow.

How would you suggest I test the NTC?

 

[Gas2Air]

Multi meter? Mate if you don't know how to check a thermistor then why should I help?

Test on Ohms, usually the HW NTC gives a lower reading on heat produced. Readings at 50+ expect 3-4 ohms, less than it will be higher.

They block easily too. So be prepared to take hose out and clean.

 

[Abcplumb]

Multi meter? Mate if you don't know how to check a thermistor then why should I help?

Test on Ohms, usually the HW NTC gives a lower reading on heat produced. Readings at 50+ expect 3-4 ohms, less than it will be higher.

They block easily too. So be prepared to take hose out and clean.

Why should you help.......aammmm maybe coz you're a nice guy and like sharing your knowledge?

I thought you may suggest a smart way of testing it through the diagnosis menu.

Anyway I appreciate you pointing me in the right direction.

 

[The831Bunny]

You need to check D.40 & 41 has a delta T of 18-20C. The DV is not passing to Heating, and the DHW flowrate is 7 L/min. You'll find at least one of these is not correct.

 

[The831Bunny]

DHW temperature can be checked at D.3

 

[Abcplumb]

Thanks 831Bunny

The DV is good, even after running the hot water the heating pipes didn't heat up.
I'm suspecting the NTC, but will check the temperature differential between the flow and return and the ohms
It's hard to image a blockage issue as the dhw plate was very clean.

 

[Abcplumb]

Turned out to be a weak pump.
Replaced the wilo pump to a new grundfos pump and all is good.
I was also told by Vaillant technicals that there isn't a way of confirming its the pump.
All 4 NTC's where fine.
Flow rate was around 6.

 

[Agile]

I would disagree with Vail Tech.

Easy to do the finger test on the pump!

In fact, although I don't, many feel the torque with a screwdriver rather than undoing the head.

You cannot do that very well on the Grunny because there is not a defined slot but on the Wilo its a very good slot!

I always remove the head because a blocked impeller is another common cause of the effect of a weak pump!

 

[GuessMan]

Pray tell, Agile how you get a Vaillant EcoTec pump to run on a drained system?

To the OP did you wash the rubber hoses out? They are probably blocking and reducing the flow.

 

[Abcplumb]

Never tried running the pump on a drained system

I didn't clean the hoses as the magnaclean only had very little sludge on it, and the filter was also clean.

I did press the hoses and the were NOT firm like the once which have sludge in it.

But I do agree I should have done the screwdriver pump test.