Vaillant 824 combi hot water

[Agile]

Its a stepper motor so not so easy to test electrically unless you have a scope.

Just possibly the ball is stuck?

You could try unscrewing the collar on the actuator and twisting it to open the ball and socket and then see if the actuator moves on its own. This is a bit trickey and you might get into difficulty!

In any case you imply the boiler is not responding to DHW demand. If the aquastat is really OK then the PCB might be faulty?

Tony

 

[CorgiIOW]

PCB U/S,,, if you have exchanged the D/ Valve

Dave .

 

[pannierstan]

The diverter valve is mounted at an angle so you could describe the movement in the vertical or horizontal directions.

I chose the horizontal as I thought that would be the easiest to understand.

Tony

The valve is mounted so the movement direction would be up and down.
Undo the large nut ontop of the divertor valve that holds the black plastic assy in that has the 4 wires coming out of it.
This is the motor that drives the rod Agile was reffering to. If you withdraw it carefully it should be connected to the end of the shaft. Pay attention to how it connects in a sort of ball and cup arrangement.
While the motor is in your hand you can actually try heating and hot water to see if it moves but make sure you leave it in DHW demand or you will not have enough play to reattach it to the rod

If you are sure they are engaged then as Agile said you are not sensing DHW demand which would suggest the aqua sensor. Ignore the preheat for now and make sure it is switched off.

The simple answer is that if the Preheat is off and the heating is off. If you turn on a tap and nothing is happening the boiler does not know you have turned it on SIMPLE. In which case it has to be the Aqua sensor impellor or Hall effect sensor or somewhere between it or the PCB.

Are you O.K with a volt meter as I can tell you how to check that the Hall sensor is sensing other than that do you have a digital display on the front panel or just 3 lights.

One 1 occasion only I had a motor which was burnt out and on 1 occasion I have actually had a board that was not driving the motor. ie V.rare.

Stan

 

[peitho]

Hi, I tried conecting the old diverter valve top to the connection rather than take the new one apart. The shaft spins when you switch the heating on & off but there is no response when you turn a tap on. I have a diagnostic panel on the front, which i think I tried before and found that the boiler did not recognise that hot water was being called for , hence the replacement aqua sensor.
Tony

 

[Agile]

Hi, I tried conecting the old diverter valve top to the connection rather than take the new one apart. The shaft spins when you switch the heating on & off but there is no response when you turn a tap on. Tony

I think that the diverter rests in the DHW position so you should not expect it to move when DHW called for if the heating is off.

However, if the PCB is not showing a demand for heat then either the aquastat is not working or the PCB is faulty ( or the leads! ).

Have you checked the continuity of the leads to the aquastat? You must check continuity with a low impedance check and NOT a high resistance measurement.

Tony

 

[peitho]

Hi, I've just done the self diagnostic tests again -
d.22 DHW demand with tap open 0= no
d.25 Hot water activation via warm start clock, with warm start off 1= yes
d.35 Diverter valve position with heating OFF & tap open= heating system.??

I will need to borrow a meter and possibly a mate to check eclectrical continuity.
Tony

 

[pannierstan]

The actuator actually rests in whatever the last demand was but thats irrelivant as your boiler is not sensing that you have the tap on.

When you get a mate and a meter you will need to check between the red/black/green wires

Red is 5v+
Black is ground
Green is pulse

If you put your meter between the green and either other connection with the tap running and you get 2.5-3.0v then your aqua sensor is fine and the board is buggered.
If you go between the green and any other colour and you get 0v or 5v then the aqua sensor is NOT turning.

Stan

 

[peitho]

Hi guys, Ive got the meter. With black pin on the green wire & red on red I get a reading of 9.6. With red on black I seem to get no reading at all.
Does this help us?
Tony

 

[Strachan]

You should be getting a reading of 2.5Vdc checking green and black, and the same figure checking green and red when the tap is running.
Check the red and black with the tap off.

 

[peitho]

With the tap off the red & black read 9.6.

 

[Strachan]

Looks like you`ve a supply fault to the aquasensor. How old is the boiler?

 

[peitho]

about 5 years old.

 

[Strachan]

Agile is probably correct (as usual) it being the pcb by the sounds of it. If the leads were faulty i`d doubt you`d be getting a higher reading than normal. You`re getting the same reading for the closed and open position. This should not be the case.

 

[peitho]

If I take a reading as the wires come out of the PCB would that confirm the diagnosis?

 

[Strachan]

Best get an engineer out, ask them if they`re familiar with this boiler, and be cheeky and ask if they do a "no fix no fee". Then you`ll probably only get one to show up who`s comfortable in the knowledge he/she (politically correct) will be able to diagnose and fix the problem.