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Hello All

Been watching and benefiting from the forum (and UH's videos) for years. Time to register...

So I've got an Intergas HRE boiler open vent. It was working fine as a heat-only boiler via the 240V switched live on X2 port 1.

Today, I put in a "test rig" which consists of a Nest 3rd gen and heatlink temporarily located next to the boiler so I can try different settings etc. I've got at least one MV open manually and the pump running so if/when the boiler fires no harm done.

So my first attempt was to connect the Opentherm pair up for CH and have the HW control the boiler via the X2 port 1. At first I thought it was working but then I realised that if for example opentherm is running the boiler then it gets 240V on port 1 the boiler shutdowns down the flame and restarts (its goes from its state 5 to state 2 and then back up to 5). That doesn't feel ideal or efficient. Also the two could get out of sync quite easily so you could quite easily get a situation for example where who controls are signalling "OFF" but the boiler is still running - rectified by moving one of the controls to ON and then OFF again.

So, a little defeated (as I think if the boiler could cope with that I'd have a great setup with Opentherm running over S-Plan and no need to buy a ridiculously expensive normally-open MV to move to X plan). So I thought I would try the boilers low voltage controls for HW on the X4 block. The X-plan says to use ports 9 and 10 across a switch (a stat or a programmer presumably) so I connected those to my nest (ports 5-common and either 4 or 6 I'm not sure). I've tried setting Nest HW to be Opoentherm or on/off but in both cases nothing happens when I turn on the HW on the nest. The boiler does nothing. Now I've just seen manual says a roomstat should be connected on 6,7 and yet the Intergas docs for X plan say 9 and 10 so a bit confused.

At this point I'm not worried (yet) about how the MVs and pump are going to be triggered but suspect I will need paramA and a couple more ports. But not looking at that yet as I don't understand closing/opening ports 9 and 10 doesn't trigger the boiler to turn on.

Any thoughts that don't include phoning a GSE gratefully received !

Well, here are my thoughts Plugs.

I went wrong by not pressing the "tap" button on the front console to turn on HW mode. Such a simple thing to do and it makes the world of difference.

The wiring attached seems to work. My only slight concern is that if the wiring centre loses power or malfunctions for whatever reason it could start the boiler with pump off and valves closed. There is a straight path to the vent and presumably starting a boiler without water being pumped would just mean it shuts down a minute later as the water overheats but not sure.

Massively simplified diagram especially around the MVs where I've only showed the switched live going in at the top and the switched/relayed output (orange wire) at the bottom.

Interesting to see someone actually using OpenTherm, I don't have the option with an oil boiler, I did look at EPH with the master/slave system, and did note how the motorised valves are used with OpenTherm.

However clearly a motorised valve is on/off, where OpenTherm is up/down, so unless there are a lot of motorised valves, think EPH can deal with 10, can't see how they really work together? I note Wiser has a warning

Note: communications module works only with Wiser kit 1, systems (heat only) The communications module will not work with systems with a separate hot water cylinder (kits 2 and 3) even if the communications module is present.

I am told it will work, in spite of the warning.

My mother did have a modulating boiler, but no ebus connection option. I did use electronic TRV's and the boiler did seem to modulate as it should, so radiators stayed warm, rather than alternating between hot and cold, and it did seem to stop any hysteresis, however the anti-hysteresis software in the TRV heads was a bit OTT, so would set to 22°C at 7 am then 20°C at 8 am or it would be 11 am before it finally settled at 20°C.

My old house was open plan, and I am sure Nest would have worked well, but Nest Europe (Not USA) does not have sensors to go in each room, so it needs to be in a ground floor room, as heat raises, with no alternative heating including sun through windows, in a room kept cool, so that it fires up the boiler so the non linked TRV's can control other rooms, so rather limited as to what homes it will work in.

So the big question is if having OpenTherm with a thermostat that only controls one room, is worth having? Maybe it is, so I hope you will report how well it works for you.

I wanted to monitor gas use with mothers house, but no smart meter, and even these only show in half hour blocks, what I wanted is something like a clamp on meter for gas, so I could see what it used, timing how long it takes to use a kWh is not really what one wants, need to see it has modulated. Her gas bills were lower than my old house, but I had a boiler fitted around 1981 so not really efficient, and this house uses oil.

So why have you gone for a thermostat which does not connect to TRV heads? I know why I fitted Nest Gen 3, one I thought it would connect to TRV heads, and two only had two wires main house to flat with boiler, so was only way to control DHW and CH plus power the thermostat with just 2 wires. Since fitted wiser in parallel so now can start adding linked TRV heads.