Making my central heating and water smart with Shelly - need an electrical relay.

elsmandino

Morning all.

Apologies in advance for the technical nature of this post but I have a Y-Plan central heating and water system and I have bought one of these devices to make it smart:

Shelly 2PM Gen4 | Dual Smart Relay with Power Monitoring & Matter | Shelly Europe

There is a slight issue, however, in that the Shelly has two SPST-NO relays in it.

This works perfectly for the central heating side as the heating is either on or off.

On a Y-Plan, however, things are slightly more complicated with the hot water side as I need two separate contacts, as this is needed to control the actuator. Ultimately, I need an additional mechanical SPDT NO relay, 230v 10A relay.

Can anyone advise which one to get?

There are some many variants out there.

grumpy_codger

Just curious…

What other device will control 'Shelly' making your system 'smart'? And how will this be better than a normal smart CH+HW thermostat?

tacpot12

It would be easer to advise you if you can post a wiring diagram of what you are trying to acheive. If you start with the system diagram from here it will be easier to see what you want: Y Plan central heating system

elsmandino

https://forums.moneysavingexpert.com/discussion/comment/82093422#Comment_82093422

Morning grumpy - I have a server running Home Assistant, which automates everything in my home. There is an integration for Shelly relays, so Home Assistant should give me so much more flexibility than I currently have - e.g. the ability to automatically turn off the heating when nobody is home, boost hot water timer by more than an hour etc.

https://forums.moneysavingexpert.com/discussion/comment/82093541#Comment_82093541

Morning tactpot (great names on this forum) -

y_plan_wiring_diagram.gif

This is exactly what I have. The programmer bit is the area I want to replace with a Shelly relay. Connections 2 and 4 are the central heating side and are easy to deal with as Connection 2 is not connected to anything. I can therefore just connect Connection 4 when I need the heating on.

However, Connections 1 and 3 (for the hot water) are slightly more problematic as it involves a connection that flips from 1 to 3 when power is introduced. The Shelly does not have this built in, so I need a separate relay that flips between these two connections but does so when the Shelly sends a signal to do so.

Hope that makes sense - it seems Y-Plan heating systems are very clever but quite difficult to get your head around, electrically.

Heedtheadvice

I agree with tacpot. It is unclear to me why you need 3 switched lives so a diagram of the required connections for the Y valve actuator would useful.

Typically the connections on a 3 port valve are:

• Blue: Neutral
• White: Heating/Hot water mid-position or heating off/on control (Live in 1)
• Grey: Hot water off signal from cylinder thermostat (Live in 2)
• Orange: Switched Live output back to fire up the boiler and pump [1, 2]Soo

So two switched Live inputs to valve which you already have from your Shelly .... or am I missing something?

elsmandino

https://forums.moneysavingexpert.com/discussion/comment/82093920#Comment_82093920

Hi there.

The issue is that the Shelly on has the ability to connect one input with one output per channel. If there is no signal, no connections are made. With the hot water side (i.e. connections 1 and 3), either connection 1 or connection 3 must be connected for the system to work - i.e. it will not work if neither are connected. Ultimately, therefore, I need an additional relay that flips between these two connections and controlled by the Shelly itself.

grumpy_codger

https://forums.moneysavingexpert.com/discussion/comment/82093909#Comment_82093909

Home Assistant should give me so much more flexibility than I currently have - e.g. the ability to automatically turn off the heating when nobody is home, boost hot water timer by more than an hour etc.

My smart thermostat (with an app) does all this. Plus geofencing. Honeywell Lyric T6R-HW. I'm sure other thermostats can do the same, but when I checked few years ago mine was the only one with free geofencing.

QrizB

I need an additional mechanical SPDT NO relay

I don't think there's any such thing? A SPDT relay has both NO and NC terminals.

As for choosing a relay, a lot will depend on the form factor you're looking for.

If you're putting this all in a DIN enclosure, for example, you might want use something like this:

https://uk.rs-online.com/web/p/power-relays/1916071

But if you're hoping to hide it inside a wiring box, you might prefer something else.

Section62

https://forums.moneysavingexpert.com/discussion/comment/82093920#Comment_82093920

On a Y-Plan system you need a controller with an additional output for "HW off". The grey/HW-Off wire of the mid-position valve needs to be energised in order for the valve to move to the CH-only position.

This is because the hot water off situation can occur either because hot water isn't wanted (the programmer for HW is 'off') or because the cylinder is heated to temperature and the cylinder stat has gone to 'SAT'.

In the first case there needs to be an output (live) from the programmer to take the mid-position valve to the HW-only position. The lack of voltage on the programmer 'HW On' terminal won't achieve this.

Hence the need for the programmer/contoller to have three outputs.

FreeBear

You don't need any double throw relays. Simply have one Shelly to energise the valve, and another to call for heat from the boiler (or a single Shelly 2PM or a Sonoff Dual). Leave Home Assistant to work out which relays to enable, and what order.

*) I've been using HA to control the heating for quite a few years now, both an antiquated Baxi back boiler, and now a Viessmann combi via OpenTherm. Also have a bunch of sensors dotted around the house to record temperature to help with fine tuning the heating schedual.

elsmandino

https://forums.moneysavingexpert.com/discussion/comment/82094047#Comment_82094047

Thanks for this. You are completely right - a SPDT must have both NO and NC terminal, anyway.

That suggestion looks exactly what I am after. I might have to do some measuring and, as you say, consider something smaller to try and fit it inside a junction. The specs, however, are perfect.

https://forums.moneysavingexpert.com/discussion/comment/82094230#Comment_82094230

Freebear - I think you might have a slightly different set up to me. The Y-plan system is pretty old and, I am told, not used anymore.