Control warm water supply of central heating with heatpump boiler

[Sjakie2020]

Hi,
I recently installed a 300l standalone heatpump boiler for my warm water supply. Although standalone, it is still connected to my central heating system via a diverter valve. So in one of those rare cases that the whole family decides to take a bath after each other, we won't run out of warm water...

Everything is working perfect and we don't use gas for warm water anymore. Only problem I have is when there's warm water demand, my central heating system is starting up for warm water supply because there's always a little bit of cold water left in the pipes before the diverter valve switches and bypasses the central heating system. Central heating is starting up, using a tiny bit of gas and shuts down again. I'm not worried of the gas, but I am worried about all those starts and quick stops will end up bad for my heating system. The diverter valve is placed as close as possible to the heatpump boiler by the way.

I'm looking for an OpenTherm solution to switch of the warm water supply of my central heating system when water in the heatpump boiler is >50°C.
My old heatpipe boiler (Itho Daalderop) had this option and was mounted between my room thermostat and the central heating system. Whenever the warmwater supply of the boiler was warm enough, the warm water supply of the central heating system automatically switched off.
Hope you guys can help out with a simple and 'set and forget' solution!

Thanks!

[fox]

Hello,
I think this will be easy to do once DHW blocking is implemented! This is just one bit to set to 1 (or 0?) in the master status, and hot water production will be disabled.

But it's not a feature documented in the OpenTherm specification 2.2, it came later. I know that my boiler supports this, but it's implementing version 4 of OT. Do you know which OT version is supported by your boiler?

[hvxl]

The boiler should report the opentherm version it supports via MsgID 125. Use the PM=125 OTGW command if the thermostat doesn't request it. If the boiler responds with Unknown-DataID, it is 2.0 or older. DHW blocking was added in version 2.3.

But that is not a 'set and forget' solution. Normally the equipment that usually takes care of heating the water sends it when it is able to provide the service. If it is unable to provide enough warm water, it stops sending the DHW blocking bit. Of course that will only work if the devices are interconnected via opentherm.

[Sjakie2020]

Thanks, I'm new to this 'game' so not totally clear to me what has been written, but I'll sort that out!

Good to know that the heatpump boiler has no OpenTherm connections, it's just a 'stupid' boiler...

But I can use a relais with a NTC to measure the water temp and based on that temperature the relais will give an on or off signal which should trigger the the OpenTherm signal to switch off warm water supply of my central heating system.

[hvxl]

I guess I will need to add a GPIO function for sending DHW blocking then.

[fox]

How about a serial command, like the other controlling bits of the master status?
(CH, DHW)
They would be in the same "family", with the winter/summer mode and the DHW blocking.

[hvxl]

A relay doesn't send a serial command.

[hvxl]

Firmware 6.3 has new commands to force summer mode and DHW blocking. It also introduced a DHW blocking GPIO function.