Vaillant ecotec Plus 937 repairs


I have created this page exclusively regarding the Vaillant ecoTEC Plus 937 boilers. This model has now been superseded by the Vaillant ecotec Plus 938.

Unlike the standard Pro and Plus combination boilers that Vaillant offer, this model is a slightly different variation of these boilers. The Vaillant ecotec Plus 937 is essentially based on the ecotec Plus 837. The 937 is more complex, has more components and often suffers from issues that don’t affect the other models in the same way. The 937 was designed for better hot water performance which meant greater complexity in the design.

As such, among some of the extra components found on the 937 include an extra printed circuit board, extra pump(actoSTOR pump), extra expansion vessel and two hot water storage tanks.

The extra PCB controls the speed of the extra acoSTOR pump, which circulates water around the plate heat exchanger. The extra expansion vessel is needed to accommodate the extra bit of pressure created when the hot water storage tanks are heated.

Vaillant deemed it necessary to install the flow-sensor(detects a running tap) or AQUA SENSOR, as Vaillant likes to refer to it as, right above the actoSTOR pump, making it the most difficult component to get access to should it need replacing, but thats another story.

There also are several other minor components. The boiler is also much larger in terms of depth to accommodate the storage tanks and extra components.

The ecotec 937 suffers from all the same basic faults that affect the junior models, which include all the common faults like the F.75 fault. However it typically tends to have its own set of problems when it comes to the hot water side of things.

Pinpointing the cause of hot water problems with this particular model is usually more difficult. This is due to the extra complexity of this boiler, but also due to the generally poor understanding and lack of experience that most “engineers” or gas fitters have have fixing these boilers.

Vaillant 937 actoSTOR pump printed circuit board


One of the most common problems with this boiler is due to the failure of the actoSTOR hot water pump, which is partly responsible for the hot water delivery. When this pump fails it usually results in intermittent or no hot water at all, followed by the F81/F91 fault codes. However these fault codes can also be indicative of other problems with the boiler.

So whoever is attempting to fix the F81 F91 fault code could find themselves with the exact same problem after going through the pain, time and expense of replacing the actoSTOR pump if they misdiagnose the fault.

The secondary actoSTOR pump is usually time consuming to replace and retails at well over £200. In instances where a 937 has not been installed as per the manufacturers instructions, the boiler usually has to be physically removed from the wall to gain access to the secondary pump and replace it. This pump gets its main high voltage power from the main printed circuit board(PCB) and the signal to run from the secondary PCB housed at the top of the boiler.

The speed on this actoSTOR pump is variable and as such the voltage from the controller varies typically between 15 and 22 volts DC.

If someone is guessing with the F81/F91 fault, they would usually be right looking in the right direction if they look at replacing the actoSTOR pump. However other components can also be responsible for this problem as well, including the main PCB, the speed controller pcb and the plate heat exchanger which is responsible for the hot water. This doesn’t even include unlikely potential faults with the Aqua Sensor which is responsible for detecting a running tap.

This heat exchanger itself retails for around £200. So misdiagnosing this fault could result in fitting the wrong expensive part and still having the same problem. You could potentially replace both the actoSTOR pump and plate heat exchanger and still be left with the F81/F91 fault code.

Whats worse is that sometimes the failure of the actoSTOR pump doesn’t result in any fault codes showing up. Usually this happens when the pump is still working intermittently. The hot water storage tanks at the back of the boiler are designed to be heated within a set time. When the tanks fails to heat within this set time the boiler shows the F81/F91 fault codes.

However if the pump(actoSTOR not primary) is working intermittently it keeps cycling on and off and still charges the tanks within the set time period hence the boiler is satisfied and doesn’t exhibit any fault codes. When you run a tap though the pump doesn’t run consistently enough to provide a steady flow of hot water, and once the tanks are empty the water runs cold.

A blocked plate heat exchanger could also cause the same problem or contribute to it with no fault codes. This is why repairs on these boilers can be difficult to repair efficiently. If boiler spares were cheap and you could return them to your supplier once you have fitted them then it wouldn’t be so much of a problem.

Vaillant 937 actorSTOR pump failure


I seem to be fixing and more and of these 937 models with this particular problem. It seems to be that a lot of these hot water pumps are failing due to the age of some of these older models.

As such I offer a fixed price repair to remedy the dreaded F81 F91 fault. This is proving to be a popular option for my customers, as they get someone who will turn up, carries the parts, has experience fixing these boilers and can fix their problem for a set amount instead of an uncertain expense and provides a guarantee on parts fitted.

I carry the expensive secondary actoSTOR pump as a stock item for 937 repairs, which means I can potentially repair this fault the same day there and then if the pump is needed. You will not find many if any other individuals in the area I cover who carry this item for repairs. In fact one usually has to order this particular part at most suppliers as most of them don’t tend to keep it in stock. I keep this as a stock item which enables me to provide a better service.

This page has ben designed for homeowners looking for someone to repair their 937 hot water problems or F81/F91 fault code.

If you are an “engineer” or “plumber” or whatever you like to refer to yourself as reading this attempting to repair a 937 Plus then just tread carefully. If you have experience fixing regular Combi boilers, especially Vaillant combi’s then this experience can only help you.

The key is in identifying if the problems exist on the primary side of the boiler(blocked filter, blocked rubber tubes if applicable, primary pump), or the secondary side(actoSTOR PCB, actoSTOR pump) or the plate heat exchanger where they meet in the middle and sort of share responsibility.

If the boiler doesn’t fire up when a tap is running usually means there is an issue with the Aqua Sensor or primary PCB.

Vaillant 937 actoSTOR pump situated bottom right hand corner of boiler


If you are attempting repairs on boilers then please note that the information on this page may not be accurate. As such, any information from this web page and website cannot be relied upon when attempting to carry out your own repairs. Repairs on gas boilers in the U.K. should be carried out by heating industry professionals who are competent and Gas Safe Registered. Please read my disclaimer.

Richard contact numberemail address

Areas where I can service & repair your Vaillant ecoTEC Plus 937 boiler

areas that are covered

I am located in Elsecar, Barnsley, South Yorkshire. I cover a large part of South Yorkshire including most of Sheffield, Rotherham and Barnsley. I also cover a small part of Doncaster.


I cover most of Sheffield including central Sheffield, Chapeltown, Ecclesfield, Grenoside, High Green, Oughtibridge, Thurgoland, Wortley, Aston, Aughton, Swallownest, Todwick, Hillsborough and Stannington.


I cover the whole area of Rotherham including central Rotherham, Brinsworth, Catcliffe, Canklow, Masbrough, Treeton, Whiston, Greasbrough, Kimberworth, Thorpe Hesley, Rawmarsh, Wentworth, Bolton-on-Dearne, Goldthorpe, Thurnscoe, Wath-on-Dearne, Mexborough, Swinton, Kilnhurst, Hooton Roberts, Ravenfield, Thrybergh, Bramley, Hellaby, Maltby, Thurcroft, Wickersley and Braithwell.


I cover most of Barnsley including central Barnsley, Birdwell, Stairfoot, Worsborough, Kendray, Ardsley, Athersley, Monk Bretton, Lundwood, Royston, Brierley, Cudworth, Cortonwood, Great Houghton, Shafton, South Hiendley, Brampton, Darfield, Wombwell, Hemingfield, Elsecar, Hoyland, Jump, Barugh Green, Cawthorne, Darton, Dodworth, Gawber, Mapplewell, Pogmoor, Staincross, Wilthorpe, Worsbrough, Thurnscoe and Tankersley.


I cover a small part of Doncaster including central Adwick, Conisborough, Edlington, Warmsworth and Mexborough.