Vaillant 824 combi hot water

[peitho]

My heating is fine but on the hot water side when you open a tap the boiler does not fire. I have replaced the aqua sensor and now the diverter valve. Now I can get hot water if the boiler is set to warm start but it still does not fire if set to normal when a tap is opened. Any ideas?

 

[Strachan]

ecotec?

 

[pannierstan]

. I have replaced the aqua sensor

There are two parts to the Aqua sensor so have you replaced the impellor and housing or have you just replaced the small black Hall sensor with 3 wires which clips into the housing.

The only reason you are getting hot water during the warm start is that the boiler is trying to heat up itself!

I have never know a Hall sensor fail as they are a Solid State device so have no moving parts but the impellor can stick. Its held in by a circlip straight infront of you.

What model is it

 

[Agile]

I have always managed to take them apart and clean them out under running water.

I agree the Hall effect sensor should be very reliable but there is also the lead and connector to the PCB to consider.

If I am suspicious of a connector I exercise it a few times and put some silicone grease on to keep oxygen away from the newly scraped metal contact surfaces.

Tony

 

[peitho]

Hi, Its the whole aqua sensor that I have replaced! I have tried cleaning the electrical contacts. I don't know if this helps to diagnose the problem but- if you put the boiler on warm start without the heating on then the rads get warm!
Tony

 

[Agile]

It sounds as if your diverter is faulty. Thats a common fault on your model.

You say you have replaced it but was it a genuine new one recently made with the elongated ball and large weep holes?

Tony

 

[pannierstan]

And have you made sure you correctly engaged the motor shaft onto the rod of the valve

 

[peitho]

Hi guys, yes it was a genuine vaillant part. I don't know about the elongated ball. There didn't seem anything needing to engage. It was 2 compression joints to water pipes and a clip on to the secondary heat exchanger! ??

 

[Agile]

There are two holes at 180° to each other between the actuator and the operating manifold. Were the holes on the new valve larger than the original?

Presumable you plugged in the electrical connection properly?

Using a fibre optic light can you see the shaft move through the hole when selecting between HW and CH ?

Tony

 

[peitho]

Hi, Yes the holes are larger than on the original. I've tried a torch through the holes. It dosen't seem to do anything at all when calling for water?

 

[Agile]

It "rests" in the DHW position towards the left.

It moves towards the right when CH is called for.

Well at least thats what it should do !!!

Tony

 

[Agile]

Hi, Its the whole aqua sensor that I have replaced! I have tried cleaning the electrical contacts. I don't know if this helps to diagnose the problem but- if you put the boiler on warm start without the heating on then the rads get warm!
Tony

It sounds to me as if there are two faults!

The boiler is not responding to a DHW demand

AND

The diverter is not moving to DHW position.

I dont remember the arrangement but could the aqua sensor have been fitted the wrong way round?

Tony

 

[peitho]

Hi guys, the sensor nor the valve can not be fitted the wrong way. I can't see what you mean by the valve moving left & right. I would expect it to go up & down the shaft?

 

[Agile]

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

 

[peitho]

Thanks , but I'm afraid its not moving any way.
Tony