The Efficient Home Forum

OK, so again Ideal and Resideo (Honeywell Home) seem to argue over the correct way to install the evohome OpenTherm Bridge on an Ideal boiler...

So, the best document I can find is this one from Ideal (as their Boiler Installation Guide details on the OpenTherm connection is useless) - https://idealboilers.com/uploads/docume ... _Guide.pdf

In this guide for their own OpenTherm thermostat it states...

"*Where the Ideal Touch kit is being fitted to an existing installation (S or Y plan), the wire
connecting any SL IN on the boiler requires disconnecting and making safe. A link wire
should then be connected into the SL1 L-IN connection at the boiler*.
For further details refer to the boiler installation and sevicing instructions.
*Logic Heat H, Logic System S, Vogue Gen2 System"

To confirm, you should have no other wires attached to the Weather Compensation terminals or the 230v SL2 and your wiring should look like this below...

The 230v side should look like this... The OpenTherm terminal should look like this (link wire removed and then two wires attached to the OpenTherm terminal and then the same two wires attached to the OpenTherm Bridge)... Once you power the boiler back on, the OpenTherm Bridge should 'flash' either a red light OR a green light every 10 seconds (depending if the OpenTherm Bridge is pre-bound or not).

If you have any questions, please ask.

Hi

I'm having my boiler replaced by a Logic Heat. I already have Evohome so if I want OpenTherm is it just a case of swapping out the heating BDR91 with a R8810A1018?

Thanks in advance.

Somebody wrote:Hi

I'm having my boiler replaced by a Logic Heat. I already have Evohome so if I want OpenTherm is it just a case of swapping out the heating BDR91 with a R8810A1018?

Thanks in advance.

Yes, you would need to change the boiler demand BDR91 with an OpenTherm Bridge.

You do need to understand that an OpenTherm system operates quite differently to on/off switching system and therefore traditional heating system configurations (S & Y Plan) are not ideal for modulation system conversions.

The EVOHOME Shop wrote: You do need to understand that an OpenTherm system operates quite differently to on/off switching system and therefore traditional heating system configurations (S & Y Plan) are not ideal for modulation system conversions.

Thanks for the response.

Why do you say that OpenTherm is not ideal for S & Y Plan systems? Surely modulating the output continuously to match the exact heat demand is good, as is letting the boiler operating at full condensing mode for longer, both saving energy? Is it something to do with the hot water prioritisation? What other factors should come into consideration please?

Thanks again

Somebody wrote:Is it something to do with the hot water prioritisation? What other factors should come into consideration please?

Thanks again

S & Y Plan systems were designed in a time where water temperature for heating and hot water was the same. With OpenTherm, space heating can be at a very different temperature (maybe 30 Deg C) to what is then required for hot water reheat (70+ Deg C). There are other factors too, but this is the main reason why S & Y Plan systems are bad system design if you are considering going over to OpenTherm.