I have a Centrometal pellet burning central heating boiler. It works much like a combi and has a built in pump. I bought it secondhand and it works OK but the furthest rads stay cold. The same rads worked OK with the previous log fired boiler so I thought there might be a problem with the pump electronics. It is a Wilo pump but a model with no speed knob. I took the pump apart with a view to bypass the electronics and run it at full speed. I am now thinking it has been installed the wrong way round (I have only ever removed the motor section, not the whole pump). It is on the flow side so I would expect the arrow to point away from the boiler. The iron pipe at the bottom of the image is the flow outlet at the back of the boiler.
![20250726_151931[1].jpg](https://www.diynot.com/diy/attachments/20250726_151931-1-jpg.388015/ "20250726_151931[1].jpg")
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Pump Wrong way Round?
- Thread starter fidom
- Start date
To my mind, a pump in the flow pipework should pump water away from the boiler and on its way to heat an indirect water cylinder (calorifier) and radiators. With your pump forcing water into the boiler via the flow tapping, then your system is not working as a well-designed system should. Being that your pump is connected via unions, reverse it and the see how your system then behaves.
We sorted on of these that had been poorly installed,
The manuals were readily available on line.
The manuals were readily available on line.
Not sure what model of boiler you have but the manual for the ZVB II 16-32 has the pump on the return side.
Normally, pumps are fitted on the cooler return side of a boiler. To check from cold, the flow will become warm, long before the return, when the boiler starts.
The arrow is pointing away from the boiler,
which seems to suggest the pump is fitted the correct way.
That suggests either obstructed pipes/radiators, or that the system needs to be better balanced. What happens if you close the valves, of some of the radiators which do get hot?
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