Evohome. Moving to opentherm S plan setup with Ideal Vogue

[mtmcgavock]

Re hot water priority on existing zone valve what is the modification to make it reverse its open/close functionality. I.e what swaps with what ?

Your HW BDR91 has A, B ports and C ports. In your current situation you have probably put a link in from L to A (I'm guessing the same for your Heating BDR91). Then B goes to your hot water MV to open and close as needed.

On your CH BDR91 you need to remove the link from L to A. Then make a link from C on the HW BDR91 to A on the CH BDR91.

If you want to be even more adventurous you can add a two way switch in to turn it on and off but maybe we'll not get into that yet

[Felkin123]

Beaut ! I linked Lto A in the junction box if memory serves. 2 way switch I’m game 😀

[mtmcgavock]

Beaut ! I linked Lto A in the junction box if memory serves. 2 way switch I’m game ��

To do the two way switch you need just a standard two way lighting switch (they’re usually rated to 10amp).

From the c port of the HW BDR91 take this to L1 on the switch, take a Live feed to the L2 (this can be from L on either of the BDR91s). Then take the COM on the switch to the A port on the CH BDR91. When the switch is in one position it’s HW priority and in the other just normal operation.

I find it quite useful being able to turn it on and off, as usually I just run mine in normal operation. However if we’re wanting quick Hw recovery or have guests staying I turn it on.

[Felkin123]

Ok So I’ve added in the opentherm controller, removed the heating valve (not physically yet just locked it open and removed the wiring from the junction box ) and the switched live. The boiler fires fine and the water temperature is ticking over in the mid 40s to maintain the set points in the house. All good. I think I’ve got something wrong on the water side though. When the Water valve opens on the unvented the boiler still seems to be modulating although a little warmer on the flow and return temps 55 and 38 ish respectively and the water takes a lot longer to warm up than when it was on switched live. I’d expect the boiler to go on full demand when the water zone valve opens. Have I missed a binding somewhere? Also the controller was giving me a comms fault on the heating valve after the changeover. I have taken the batteries out for hard reset and so far it hasn’t come back.

[Felkin123]

So had a fiddle (technical term) reset rebound the water BDR specifying hot water valve only and the system has sorted itself out once up to temp the Vogue ticks over at 33-45 keeping the pump running and kicking in the burner/fan on 25% for about 20 seconds every 5m or so which maintains the 19 degree set point in the living room. I’ve noticed that this method sends less hot water round the bypass and maintains the setpoint more accurately. When the water demand kicks in I’ve had minor overshoots but I’m not sure they are any more so than when it was using switched live /full power. And it’s been much milder the last few days. Have to say first impressions of OT in Evohome are very good indeed !

[Shadylee]

So had a fiddle (technical term) reset rebound the water BDR specifying hot water valve only and the system has sorted itself out once up to temp the Vogue ticks over at 33-45 keeping the pump running and kicking in the burner/fan on 25% for about 20 seconds every 5m or so which maintains the 19 degree set point in the living room. I’ve noticed that this method sends less hot water round the bypass and maintains the setpoint more accurately. When the water demand kicks in I’ve had minor overshoots but I’m not sure they are any more so than when it was using switched live /full power. And it’s been much milder the last few days. Have to say first impressions of OT in Evohome are very good indeed !

Correct me if I'm wrong but burning for 20secs then cycling isn't what opentherm does.

What you have is the boiler going into anti cycle because there's not enough load to dissipate the minimum fire/modulation of the boiler.

There's a guy on here who had the same issue with the vouges.

[mtmcgavock]

I was also under the assumption too that there was a lot of issue with Opentherm and Ideals, as said above there is one guy on here who has had endless amounts of issues with them.

[Felkin123]

Anti cycle ? Surely the boiler is circulating warm water around the radiators and ABV and firing on minimum when required ? Before it would fire on full then switch off with a few minutes of pump over run through the ABV. To my mind the current scenario is better in all ways. It does switch off sometimes when no heat is called. So what should it be doing ? What behaviour should it be exhibiting?

[Shadylee]

Anti cycle is a timed pump overrun without burner to shed heat, it's doing this because it can't modulate any lower and has to turn the burner off to protect the boiler.

On my vokera anticycle is 3 mins,

What you have explained above is that the vouge will run at 20% every 5 mins for 20 seconds then turn off and go back into pump overrun.(anti cycle).

The whole point of opentherm is that the boiler modulates at a flow temp that it needs for the circumstances, but what is happening is your boiler can't modulate any lower (maybe due to only 1 room needing very little heat) and simply can't burn any lower flow temp.

I'd hazard a guess that the boiler is oversized for the load and it's cycling because only 1 room is needing very slight amounts of heat.

The reason cycling is inefficient is because when the boiler fires it will normally run at 75% (my vokera) for the initial startup, and every time it does this it's using and wasting gas to get going again,

there's also argument about components being used more from a wear and tear point but given how many times tpi starts and stops the boiler in a given hour I doubt it's relevant with evohome.

I thought the whole point of opentherm was to keep a slow burn, rather than on and off like tpi does?

Hopefully dbmandrake will chime in to put me right, as it's all my assumption and I'm not trained at all in this stuff.

[Shadylee]

https://youtu.be/L8CcL7SafpE

Here's the video from a fellow member on here regards to short cycling, is this what yours is doing?

[Shadylee]

And here's said thread about vouge not modulating down and cycling.

http://www.wordpress-1219309-4387497.cloudwaysapps.com/vbulletin/showthread.php?4996-Ideal-Vogue-amp-Opentherm-via-Honeywell-T6-Lyric-(wired-version)

[Felkin123]

Yes that’s what mine is doing. His is at a set point of 14 degrees. Mine is exactly as you suggest not able to modulate the burner down low enough for it to be on to maintain the setpoint in one room. So it circulates hot water WITHOUT the burner. To my mind this is a good thing and an improvement over the previous TPI setup. Especially as the pump is included in the 10 year warranty should it fail. I did read some of the other thread you posted but life is too short to read all sorry if the OP is reading this but 8 pages 😀.

[Shadylee]

My non opentherm vokera does it, I get it mainly when I'm heating the office only, but like you say it's not the end of the world, there's still heat being pumped round.

I've toyed with opentherm and weather compensation, but to be honest when I replumbed our house I oversized every radiator by 3 times with double convectors.

So my 24kw Combi is set to a max flow of 55c even in minus 4c temps outside, if I fitted weather comp sensor it would be trying to push 60plus flow no matter how low I set the heat curve.

Sometimes I think there's a finite amount to be saved once you have decent controls already.

[HenGus]

Likewise. Once the zones are up to their set temperatures, then it is often the case that the pump is just circulating hot water around the system when there is just a single zone requiring some heat. In my case, this is usually my hall/landing/stairs zone. On the coldest days this Winter, I have seen settled flow/return temps of 52/47C which over the past couple of warmer days has been in the range 43/36C. FWiW, my zones not in use are set at 13C. Under OT, I am seeing some initial temperature overshoots with optimum start but, once settled, the temperatures hardly vary. I resist the temptation to fiddle as fiddling invariably results in a high flow temperature/high gas usage.