Strange boiler behaviour...help required !!

[nileshpatel]

Hello, I have just moved into a house where we have a Vaillant VCW GB 280 H Combi-boiler fitted.
This is my first experience of an 'older' combi-boiler but we have strange going-ons here...let me explain....
1. We have a Potterton programmer which has a timer for CH and HW - being a combi boiler, does it really require a timer for the HW as I assumed that hot water is available on demand.
2. In the kitchen, I only get HW when the HW is activated on the programmer - if the programmer says NO then NO HW. BUT if the programmer says YES then YES I get HW in the kitchen...but only for around 30 seconds and then nothing - regardless of how much I open the tap. Switching the tap off for a few seconds then on again gives me HW again, but only for 30-ish seconds.
4. Bathroom....different story here...when the tap is opened, I get hot water...any time of the day, regardless of the state of the programmer. If the tap is left open (i.e. to fill the bath tub) then the hot water will flow continuously. I believe that there is no additional tank anywhere in the whole house (even the loft), just a badly behaved boiler, I believe.
If anyone can shed any light into this matter then I will appreciate it greatly and if anyone can suggest any further test then let me know.
Ta !!

 

[JohnBailey]

I'm not an expert, and can't comment on the controller settings, but the difference between kitchen and bathroom tap behaviour could possibly be down to flow rate. Perhaps the kitchen has a slower flow so boiler cuts out to prevent overheating. Does the kitchen tap have one of those screw-in airator things? if so try it without.

 

[nileshpatel]

Thanks for the info but no aerator on this box standard kitchen tap.
Could the boiler trip out even when the tap is opened fully ? I'll report the flow rate of the hot water tap in full flow but it looks as though the water flows much quicker in the kitchen than it does in the bathroom.

 

[Slugbabydotcom]

Could be the beginning of the end for your flow switch diaphragm.

 

[Agile]

Turn the kitchen hot tap AND the bathroom basin hot tap both on together and tell us what happens!

Tony

 

[Deleted member 105431]

Call vaillant out for a fixed price repair. You may need a new water valve and servo.

 

[DP]

Boiler is open flued. Might be an idea to get it serviced pronto. Not a 5 minute job but as detailed in the manual.

Boiler complexity means many claim to know the boiler but few who are able to perform the task.

 

[namsag]

Firstly its wired up wrong with a programmer and needs a single channel clock and a permenant L N E to the boiler.
As for water problem it will be the diaphragm in the water section starting to wear and needs replacing .
Couple of simple jobs for someone who knows vaillants

 

[nileshpatel]

I'll check the wiring tonight (I have the original booklets) and see what is correct and what isn't.
Will also open bathroom/kitchen taps and report back.

 

[nileshpatel]

...after a further look, I see that the pressure gauge is reading very low, way below the red pointer and the temperature gauge isn't working at all.
I'll call in the experts and take it from there.
Thanks for the help !