Drayton wiser opentherm and hot water

[fezster]

Searched for an answer to this but couldn't find anything relevant.

How does the drayton wiser system manage hot water when using opentherm? Evohome has a cylinder kit which monitors the tank temperature and adjusts HW flow temps to 80 degrees. Doesn't look like the wiser has anything similar. So how does it work?

[HenGus]

Evohome has a cylinder kit which monitors the tank temperature and adjusts HW flow temps to 80 degrees. Doesn't look like the wiser has anything similar. So how does it work?

Evohome Opentherm control does quite work like that. When there is a HW demand, Evohome will demand c.90C flow from the boiler. This should be limited to TMax Set (or equivalent) in the boiler set up parameters. For example, on the Atag that I used to own, TMaxSet was 70C. The boiler flow temperature would be restricted to this limit whenever Evohome asked for HW re-heat.

Unfortunately, not all boiler types limit the HW temperature demand in this way. For example, one of the Viessmann boilers has issues.

Sorry, I know nothing about Drayton or Nest but I would have thought that the principle would be the same as the same Opentherm protocol is being used

[fezster]

The Wiser manual is sparse on info, but it does say this:

The Wiser Heat HubR is an OpenTherm certified product and will therefore operate with OpenTherm certified boilers. Currently The Heat HubR is not compatible with boilers that require a temperature for domestic hot water to be provided by the external heating controls.

Which indicates to me it does not boost the flow temp to max on HW, but it's not entirely clear.