Vokera Excell 96E,No hot water When heating off

[alanduncan]

I have no hot water when i set the boiler to hotwater only ,just with the Heating on, so have to have it on low for 24 hours.
I replaced the Domestic Diaphragm and the smaller diaphragm below it.
But still no hotwater when heating cuts out.
When i Switch to hotwater only i hear the pump stop ,when i run the hot water all i get is a faint glow from the Low Water Pressure LED and the same glow if i have the heating is on and the timer off.
I phoned Vokera they said it could be the pump,but when the heating starts up the rads are hot in no time. My water Pressure is very good. Help
Alan

 

[nickso]

if the pump stops when running HW, the flow switch will drop out causing low pressure warning.

ive had to change the pump for this before when it was running but not giving enough flow for the switch to make, if it runs but the flowswitch doesnt make check the venturi in the diaphragm housing first and also test the switch.

 

[DP]

Nickso, is that for the Excel?

OP, is the pump speed selector on speed 3?

 

[alanduncan]

the pump only stops when i change from CH to HW only, when the CH is on and i run the hotwater ,the pump keeps running.
When i run the heating or HW,with the water on the fulcrum moves and makes the switch, but the one below it doint come out.

Im not sure what the Venturi is in a boiler,is it the plate that pushes the Diaphragm, thanks
Not looked at the Speed, but will be set as it came 14 years ago i would think.
Its the excell 96E in the 14 years i have had it all i have replaced is a diaphragm 2 years ago
a circuit board 8 years ago and a mico switch 9 years ago
so its not been bad

 

[alanduncan]

if it is the pump, would i be right in thinking it would be about £80 for a new one and how easy are they to fit for a spark with limited knowledge of boilers

 

[Agile]

Better to start with the basics!

When you run a hot tap does the fulcrum arm get pushed by the pin?

Does it move far enough to operate the DHW demand switch at bottom left?

If not then does it bring on the boiler for DHW if you pull to top towards the front to simulate being pushed by the pin?

Just sometimes the switch lever gets a bit weak and needs to be bent a little to ensure it operates reliably.

Same can happen to the system flow switch lever but yours is not getting to that stage.

Annoyingly fiddly boilers to do any work on lower half but apart from the diaphragm pretty reliable.

Tony

 

[alanduncan]

Thanks Tony went back out for a look .
When i put the hotwater only or the CH with the clock off
The arm moves and switch clicks, then all of a sudden heard lots o clicks from the control box, looked under and the flow switch was moving in and out all the time and the Pressure and the flue LEDs lighting in turn , this is new when i put the heating back on it stops and the boiler fires up, and if i put it back to HW only this flow pin keeps coming in and out maken the control box click, is this more faults or help to find out what is wrong with it, could this still be the pump

 

[Agile]

"Went back out" ???

Whats all that about? Isn't this your boiler at home? Are you trying to repair it for someone else?

As it works OK on CH then most of the basic aspects of the boiler seem to be OK, pump, flow switches etc.

Just to be confusing, the flow switch works in the opposite direction to other boilers and counter intuitively so that pump flow causes the pin to move INWARDS !

Now we are getting to the point where I am having to start some guessing!

If the boiler is correctly set up, the power on CH is lower than on DHW as set by a CH power pot on the PCB. So my conclusion is that its a gas/safety aspect which is resulting from the boiler being on full power in the DHW mode rather then athe lower CH power. But that is something that I dont give advice on in an open forum ( in accordance with forum rules ).

Perhaps DP , who is an ardent fan of Vokera boilers, has some suggestions which, if necessary, he could post in the closed access engineer's section of this site.

Tony Glazier

 

[alanduncan]

Thanks Tony, looks like ill need to get a ARGI man in, to have a look.The boiler outside the house in a leanto.
If i put the HW only on and look underneath i can see the pin going in and out like a steam train, i take it its ment to come out and stay out or not come out at all, so you doint think this would be the pump,
another thing is its starting to drop in pressure and have to top up every 2nd day

 

[DP]

Pump works for both heating and HW. Therefore, pump will be OK as heating is not a problem.

 

[alanduncan]

Thanks DP, as vokera help line told me it could be the pump, and i did not want to spash out on a new pump if it was ok

 

[Agile]

Just to be confusing, the flow switch works in the opposite direction to other boilers and counter intuitively so that pump flow causes the pin to move INWARDS !

Tony Glazier

When the boiler is running the pin should move, AND stay, in !

Tony

 

[nickso]

not often i disagree with danny but i dont agree if the pump is ok on heating it necessarily is on HW.

i have had to replace the pump on an excell on the advice of vokera for similar symptoms. it cured the issue on that boiler, dont remember what size of excell it was though. i was sceptical when vokera suggested it, after all convention would assume if the pump can make flow rate round a heating circuit it surely can on the far smaller HW circuit.

the flow pin often pumps in and out if you have an airlock, perhaps this is related, it wasnt doing this on the boiler i repaired.

BTW, im not suggesting you go out and buy a pump on the basis that it cured my problem, i would be far happier if you got someone knowledgeable to look at it.

 

[Agile]

On many boilers the circuit resistance is higher on the DHW and so a pump can be adequate for CH but not for DHW.

That situation can be accentuated if the plate HE is partially blocked.

Very oddly they rarely get blocked on the Vokera Excell.

Tony

 

[nickso]

On many boilers the circuit resistance is higher on the DHW and so a pump can be adequate for CH but not for DHW.

That situation can be accentuated if the plate HE is partially blocked.

Very oddly they rarely get blocked on the Vokera Excell.

Tony

then we shall have to assume this is the case on my example.

ive replaced/cleaned plenty of excell PHE's. its just down to water quality IMO.