Vaillant Aerotherm plus does not reduce flow rate despite low delta T
Do I understand correctly that it should usually be lower, or does it always want to be on maximum flow for some reason, no matter the deltaT?
My fear is, that our system is completely oversized and not capable of working at such low requirements as our little house.
I assume that you have received no error messages indicating some sort of problem.
I believe that PWM controlled water pumps revert to full speed if the control signal is lost, I would therefore suggest that you check the relevant plugs and sockets on both the pump motor and the PCB.
The secondary pump won’t be pwm controlled, I assume? Why do you have a buffer and secondary pump anyway?
Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.
My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.
Thanks! No, there is no error message. The pump that I am talking about (the one producing the maximum flow rate) is the building circuit pump inside the Vaillant Aerotherm unit.
I posted this question also on facebook and from the feedback there, it seems it is the normal behaviour for Vaillant heat pumps (and Mitsubishi) to run at a constant flow rate (maximum if possible), while dT is NOT kept constant.
Interesting that you mentioned the PWM. The Grundfos UPS3 manual does go on about this, but I don't know how this would work in this context. The Vaillant controller would have to send the speed command to the unit, but I think it only switches it on and off. The speed/pressure setting of the Grundfos pump is done on the unit via a button.
It seems our unit is simply oversized 🙁
On page 63 of the attached file the diagram shows the location of the water pump (item 5, labelled Heating Pump).
Page 89 shows connector X16 providing power to the Heating Pump, while X22 initiates actuation of the Heating Pump. This internal water pump may therefore have two cables connected, one to supply electrical power and the other to control the speed. If the correct water pump has been installed with the necessary cables then I would expect the Vaillant controller to be able to vary its speed. Have you looked inside the unit to confirm what is fitted? What controller are you using?
On the Mitsubishi Ecodan I think that you will find the the water pump is external to the heat pump unit, and the controller can only vary the water pump speed if the correct water pump capable of PWM control has been installed. The controller can then set the pump speed to one of five alternative settings.
I am still trying to solve the puzzle of our low efficiency. In the meantime however I found out, that the Vaillant aerotherm definitely works with a constant flow rate, which is generally fine.
I will put my remaining conundrum into a different thread, as the question of the constant flow rate I think is answered, i.e. it's constant and that's fine, so the problem must be something else.
Thanks all!
Philipp
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