Vaillant ecoTEC Plus 937 with failed actoSTOR hot water circulation pump
This is a clip of a Vaillant ecoTEC Plus 937 displaying the F81, F91 fault code.
When a Vaillant ecoTEC plus 937 or 938 displays the F81, F91 fault code it generally means that the actoSTOR secondary domestic hot water circulation pump has failed, but these fault codes can be caused by several things.
The F81, F91 fault code on a Vaillant ecoTEC Plus 937 or 938 means that the domestic hot water storage tanks at the back of the boiler have failed to heat up to the desired temperature with the set period of time, which is five minutes.
The hot water storage tanks not heating up to the desired temperature within the set period of time can be cause by quite a few different issues but most of the time in our experience its a failed or failing secondary hot water pump.
Failure of these secondary pumps is not uncommon and we generally see this happening on Vaillant boilers between the ages of 10 – 12 years old.
These hot water pumps are not cheap and take a considerable amount of time to replace so a misdiagnosis on one of these boilers can be expensive which is why it makes sense to get someone with experience of this issue to fix your boiler.
The Vaillant 937 and 938(currently a 940 model is available) is based on the standard Vaillant 837/838 etc combi boilers, and to give you an idea of its complexity, its has two printed circuit board’s, two expansion vessel’s, two pumps, compared to the standard 837/838 etc that it is based on only requires one of each.
In our opinion the Vaillant ecoTEC Plus 937, 938 etc would have been a much simpler design with increased reliability, if it was based on a boiler design which incorporates a thermal store as opposed to an unvented cylinder(s).
Examples of these boilers with a thermal store include the Worcester Highflow range of boilers.
Boilers of this design require no more additional moving parts to achieve the same goal, which is increased hot water performance.
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