I am trying to figure out how my oil-based central heating works, as I want to adjust it properly for the winter season and possibly replace the old, energy-wasting water pumps. Unfortunately, all the components are tightly fitted in a cabinet, which means that I cannot see the connections (piping) between them. The first two pictures provide an overview of the cabinet:
Click on the pictures 😉
It is my current understanding that the cabinet contains at least the following:
- Oil burner/boiler (grey metal at the bottom).
- Hot water storage tank (green, huge, in the middle).
- Expansion tank (red, at the top).
- Manual, two- or three-way shunt valve (to the left of the bottom of the hot water storage tank).
- Pump for hot water for radiators and underfloor heating (at the bottom).
- Pump for hot tap water (at the top).
- Control unit for the temperature in the hot water tank (next to the upper pump).
- Thermometer on the supply pipe for radiators and underfloor heating.
- Thermometer and manometer on the hot water storage tank.
Close-ups of the components:
Rotated close-ups of the pumps, showing their specifications:
The pump to the left, which I suspect is pumping hot tap water, is a Grundfos UPS 20-45. It is class F and supposedly consumes 44 W when pumping. I am not sure that it is pumping continously – it might be regulated by something. If it is only pumping once in a while, it might not be profitable to replace it. According to online material from Grundfos, the current pump has to be 180 mm and a suitable replacement is their Alpha2 25-60 180 mm. The replacement, in a tap water edition, seems to cost a lot, which puzzles me a bit.
The pump to the right, which is certainly for supplying radiators and underfloor heating, is a Grundfos UPS 25-40 180 mm. It is class F and pumps continously. Currently, I have it set at position 2 out of the 3. This means that it continously consumes 55 W. If it is set at 2 for the five coldest months and at 1 for the seven other months, it consumes approx 354 kWh/year, which is approx 800 DKK/year. I have no doubt that it should be replaced. The constant, high-pressure pumping makes my radiators a bit noisy, thus replacing the pump will also increase comfort. Supposedly, a suitable replacement is an Alpha2 25-40 180 mm, which is relatively cheap in a heating edition (not for tap water). The investment will probably be recouped in two years and a few months.
I want to end up with a schematic for my central heating, however, it will require some assistance from family, friends and people in DIY forums. My quite optimistic plan is to replace the latter pump myself. It is not a simple task, as the pump is inaccessible and there are no valves next to it. I might have to drain the system for water and fill it afterwards.
Before I forget: The low temperature (approx 30ºC) of the supplied water to radiators and underfloor heating is probably due to the latter type of heating – the underfloor heating. Floors will be damaged if they are exposed to water with the same temperature as the water in the hot water storage tank, i.e. approx 60ºC. The setting of 5 out of 10 on the shunt valve possibly halves the 60ºC to 30ºC.