The Efficient Home Forum

Hi,

I am very lost now and not sure where else to get help.

I have a combi boiler. It has a honeywell relay on it.

I bought an evohome and paired it with the boiler. It had one zone called house. It turned the boiler on and off all fine. Evohome is the thermostat and is downstairs.

Now I have four new HR92s and I am confused ! I wanted to add them to the existing system so that the bedrooms could be off when downstairs was on. I know that the downstairs has to be on for them to be on, at least until I add HR92s to the downstairs as well.

I go to the config on the evohome and there is no option to add a zone, despite what the pdfs say ! I can go to the config zones, work my way through and add the two radiators that I have put the HR92s on but by then my 'house' group has disappeared.

I just wanted;

1) The evohome to control all the none HR92 radiators, by it being connected to the boiler and using the evohome as the thermostat.
2) The two radiators with HR92 to be able to come on by the temperatures set on the evohome for them. I know that that will (presumably) turn on the radiators downstairs as well as the boiler will now be on call that's fine

Am I just wanting to the impossible and the only way to do it is to have HR92s on all the radiators and then having them all in their own zones ?

Sorry if this is a ramble !

The evohome system was not designed to operate in the manor you have described... It can control a home as a single zone thermostat OR HR92's... The evohome Controller can't control the home as a uncontrolled single zone and HR92's at the same time. This is because any HR92 demand will cause the rest of the house to come on when it doesn't need to.

So when you add HR92's to a system (as per Page 43 Figure 4 of the evohome Installation Guide), the system is no longer capable of being controlled as a single zone system as the HR92's are now in control of the heat demand... This is why you are having the issues you are.

Some people have 'fudged' this with a HR92 not connected to a radiator as your 'rest of house' zone, but that is up to you and not my recommendation.

Kind regards,

Richard

I have a very similar question to the original poster.

I recently bought an Evohome Conected Modulation pack. It's working great as a single system controller with OpenTherm.

Due to the high upfront cost I wanted to add HR92 zones one at a time until my house is fully equipped, and accept that any uncontrolled radiators form part of the main zone and don't benefit, but initially I wanted to be able start with some of the more variable rooms which either need heat or don't at different times to most of my home.

Am I right in thinking that I need to start with 2 x HR92s as a minimum - one in the room where my Evohome controller is located (it can use the controller as the thermostat as the radiator is tucked behind a sofa) and then a second in whatever room I want to control independently?

I fully accept that this fudge is not a recommended configuration and means that uncontrolled radiators will rely on their current TRVs to stop them heating when any demand is registered by my boiler, but I need to find a way to gradually build my system as and when budget allows. I would imagine many people skip fitting HR92s to some of their rooms which may be rarely used and therefore a TRV set low satisfies the requirement most of the time.

You can do that. It may need some trial and error until you get the most out of the system with a less than optimum number of radiator controllers.
As a matter of fact, even now that I have all radiators automated, I am still tinkering )