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Hi everyone,
Just wanted to share my experience with "upgrading" an S plan setup to Opentherm and Vaillant Control Center (VR66). There are a few threads on a few different forums but I wanted to share a full write-up with all the steps needed, benefits and costs.
Overall, I fully recommend moving away from a simple S plan to weather compensation and intelligent controls. It enables energy savings in a few different ways.
Benefits:
Hope this helps people! I also hope gas engineers stop installing S plan with smart thermostats; it is so wasteful and inefficient (as discussed by this engineer here)
Just wanted to share my experience with "upgrading" an S plan setup to Opentherm and Vaillant Control Center (VR66). There are a few threads on a few different forums but I wanted to share a full write-up with all the steps needed, benefits and costs.
Overall, I fully recommend moving away from a simple S plan to weather compensation and intelligent controls. It enables energy savings in a few different ways.
Benefits:
- Allows modulation/ weather compensation for CH. CH should be kept as low as possible to enable the boiler to condense and modulate.
- Allows DHW priority, at a higher temperature. This leads to faster charging via a dedicated DHW charge temperature (Note: DHW charging temperature is set on boiler in the D.078, not on Nest)
- Pump overrun works to dissipate any leftover heat. In S plan mode, the valves close when there is no demand for heat, which means the boiler uses the bypass to cool down rather than the radiators. With the VR66, the valves are kept open and the heat is dissipated faster and used to heat your rooms.
- Better boiler modulation in CH. I have noticed that on eBus/Opentherm, for a given heating temperature (e.g. 50), the boiler no longer rushes to produces that exact flow temperature as soon as it turns on. Rather, it is happy to keep the burner on a lower setting and gradually build up to the temperature.
- Better boiler modulation in DHW, using the cylinder sensor rather than on/off signal. The boiler fires up differently when it knows the temperature in the cylinder (VR10 NTC sensor required). Also, you can set the target DHW temperature in Nest when the NTC is installed.
- Opentherm: this helps with weather compensation and modulation but you need to order the VR33 from this Dutch site (£70) and install it on the PCB at X31. There is also a UK stockist now. Wire this up to the OT1+OT2 terminals as shown in the instructions. For reference, Opentherm polarity does not matter.
- Thermostat. I have the Nest learning thermostat, which allows you to set the max temperature for heating, and the target temperature for DHW. It does not allow you to configure weather compensation or any other temperature curve. Any other OpenTherm thermostats should work equally well. For example, the Salus one allows you to set min and max temperatures for heating.
- VR66 (cost £100): This may be optional for combi boilers, but for system boilers, it is required. Without the VR66, the boiler does not fire when there was DHW demand from Nest, even though Nest was opening the valves. The instructions for wiring VR66 are self explanatory but once it is connected you need to bridge the RT24 terminals and remove any other connection to Nest or your S Plan box (i.e. remove RT240). Note: you just need the Earth, blue and brown wires from your valves. If you are confused about wires 4+5 coming from your valves, these are not required for wiring the VR66 - they are only used in the S plan box to tell the boiler when a valve is actually open.
Hope this helps people! I also hope gas engineers stop installing S plan with smart thermostats; it is so wasteful and inefficient (as discussed by this engineer here)
