Can I make Opentherm work with my system?

[Tim80]

Hi, 

I have an ideal combi boiler with the heating side connected via an S plan to an unvented cylinder. This gives us a hot water tank as well as direct hot water from the combi used in different parts of the house. Convoluted I know but there was only room for a small tank.  I'm now about to fit nest stats and am trying to establish if there is any way I can make use of opentherm.  My boiler and the nest are capable but if the temperature of the flow gets cranked down by opentherm it's then not going to heat my water tank properly.  It's a long shot but I'm wondering if I could use a relay to disconnect the opentherm connection when the tank is calling for heat.  My question really is whether this would mess with the nest's fragile little mind or would it not care? Does opentherm need to be set up on the nest or does it just work once wired in? Any advice would be greatly appreciated!

[AlexD]

Thanks for reaching out to us @Tim80 and thank you for all the information. I would be happy to try and assist.

You are correct, the Nest thermostat can work in open therm but it is not designed to work with systems that have a separate hot water tank, as that can't be properly controlled. You can of course control the heating side without problems.

I do not recommend disconnecting the OpenTherm connection as this will lead to an error on the thermostat. This could lead to unexpected behavior.

What I would recommend in this case, since you have a S plan system is to perhaps wire it up to the zone valves as a system boiler. This should allow you to have control over the hot water tank and heating but also leave the on demand hot water available. You can have a look here at our installation guide with some examples.

It would be best to get in touch with an installer or a Nest Pro to have a look at the system and see what the best course of action would be. Here is a link to our Nest Pro finder so you have it on hand.

[Tim80]

Ok thanks 👍🏻

[DragosC]

You're most welcome. No worries. Is there anything else that we can assist you with?

[george_t]

It's been a while since this thread was last updated so I'll go ahead and lock this thread. If you're still experiencing problems, please feel free to start a new thread and we'll be happy to help.