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Plumberpro
Plumberpro, Home Appliance Technician
Category: Appliance
Satisfied Customers: 634
Experience:  Heating and hot water heating appliances experienced
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Have a Vaillant ecoTEC plus 831 Combi Boiler which increasingly

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Have a Vaillant ecoTEC plus 831 Combi Boiler which increasingly has problems with starting in the morning. Requires many manual resetting attempts (often as many as 50) to get it to fire. Once ignited it has no problems for the rest of the day. Next morning we have the same problem. The strange thing is it seems to be affected by the weather! During hot dry summer periods it fires with no problems. When the air is humid the problems begin as do they now as the weather is getting cooler and damper. The more moisture in the air the harder it is to get to fire up. On rainy days it is almost impossible. My local heating engineer has found nothing wrong with the boiler and is puzzled. Can you help? Roger
Plumberpro
Hi ,faults lime this are a real pain . is it tyhge same on heating as it is on hot water ?
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Customer: replied 2 years ago.

Both Water and Heating are affected.
Hi , no fault codes come up?
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Customer: replied 2 years ago.

Yes F.75

OK , so F.75 Fault, no pressure change detection when start-
ing pump
Water pressure sensor and/or pump defective, air in heating installation,
too low water pressure in boiler; check adjustable bypass,
Personally I think the pump needs to be tested that is working OK . checking voltage to it upon start up .
It should be tested on ohms as well to make sure its not failing.
Also the water pressure switch needs to be tested.if that is OK,
I think just change the pump as the capacitor may be failing and not jump starting the pump .
Pumps slowly get weaker over time.
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