Vokera Excell 80SP - No hot water in morning!

[electricboy7x24]

Hi can any one help please.
I have a vokera 80sp excel 9 years old. Been serviced by B gas every year. No longer on contract.
The timer comes in at 6AM boiler fires heat up C/ heating rads fine. Then 15 minutes or so later burner goes off but pump keeps pumping hot water around rads.If you turn hot tap on during this period it will not fire.
The diaphragms and both micro switches replaced.
Also replaced the 7311(UPPER LIMIT THERMOSTAT OR INTRUPTER) as someone suggested.
Still no hot water. If I wait until boiler cools down a few minutes later it will fire and hot water is fine.
This only happens at morning.
I am an electrician so if you have any suggestion regarding checking voltages please fire away, any comment appreciated.

Regards,

Alex

 

[DP]

First of all I have to say, from past experience as a sole trader heating engineer, it is unlikely your boiler was serviced, checked certainly, serviced I doubt it.

When I attend a defect on this boiler, I would be recommending a service as dirt, dust and sedimented parts will have made the boiler sluggish to an extent where boiler fails to function correctly.

Good thing is boiler has a fault that permits fault location. Am a little surprised you as an electrician, book in hand, are not delving into boiler innards to locate the problem (manual is quite explicit) and have resorted to changing parts without foundation.

 

[electricboy7x24]

Hi Thanks for reply.I did go through the chart and all voltages were available as per manual.I also found a burnt out relay which is soldered on the pcb.I bought one from mapline electronics and replaced, as sometimes the pump wouldnt come on and I could hear clicking,but thats not the fault.
The fault only occures when boiler reaches certain temp and then cuts off but pump cary on circulating which I think is normal,but during this period no hot water is available.hot water is ok at any other time after boiler return to normal central heating mode or when its off.
thanks any way for your comments.

 

[DP]

Post your email address. Will give you pointers to locate defect.

 

[electricboy7x24]

my email is
[email protected]
thanks

Al