Updating Controls

[theboots]

We've just moved into a bungalow which has a fairly old central heating system. A Potterton Prima F boiler, a Landis & Gyr RWB2 controller and no room stat all, the radiators with the exception of the bathroom have mechanical TRV. My first thoughts were to perhaps change the controller for either a Honeywell ST9400C or a Lavatap Pro which advertises itself as a direct replacement for the Honeywell and to fit a WiFi room stat such as the the Netatmo with the thought of sometime later swapping out the TRV for the WiFi heads.

First oddity is I have only 4 connections in the backplate for the controller Live, Neutral, 3 & 4 https://www.dropbox.com/scl/fi/5wv3...late.jpg?rlkey=xa3yqqau96rvsubc4zaxq0l8j&dl=0 I was expecting to find something on #2. I figure I could interrupt #4 take out via a junction and through the contacts for a thermostat and that should work. But the modern controller I am unsure and which order to swap them. If I understand correctly the backplate should be common so a drop in replacement for the controller?

There's a junction box in the loft but it is a mess, I am up for tidying it but not in the winter and risking breaking the heating. There's a 3 port valve and two 2 ports plus the shower pump tacked in there. There's 2 hot water cylinder linked together and 1 stat on the left side one https://www.dropbox.com/scl/fi/zl84gr8w09qjjfyb7gb03/Tanks.jpg?rlkey=6mzh3d4ff6dgzn6zyaqe02md5&dl=0

I did open the boiler but again the wiring is a bit of a pickle, nothing is clearly marked,

 

[Madrab]

A Prima F - oldie but goldie.

Very strange wiring in the programmer as that would suggest that there is only one programmed control over both the CH system so the boiler runs on the same timing for HC and HW and and the HW feed is controlled by the cylinder stat and valve(s).

Not sure why there would be a 3 port and 2x2 ports either as that's just pointless too and wouldn't make sense to have both.

I think you need someone in to go through the whole system and map out exactly what is doing what, so you can get some kind of baseline and from there you can look at what controls may need to be added and how things should be properly configured to give you the control you need

 

[UpgradeME]

3 is HW on and 4 is CH on, take a look at the "Zone Valve System" wiring diagram here https://www.free-instruction-manuals.com/pdf/pa_458175.pdf and you will see how it's likely wired to the wiring center JB1 (likely in your loft?) and where to connect the room thermostat wiring.

You could verify your existing wiring against the diagram with a multi-meter and visual checks.

 

[Madrab]

Apols, was looking at a totally different wiring diagram, the RWB30, no idea why it linked to that - should know better and have checked.

 

[theboots]

A Prima F - oldie but goldie.

Very strange wiring in the programmer as that would suggest that there is only one programmed control over both the CH system so the boiler runs on the same timing for HC and HW and and the HW feed is controlled by the cylinder stat and valve(s).

I am guessing it is of the same family as the Netaheat I fitted when I was young and keen around 1985. As far as I can see the HW & CH do run independently but obviously I don't want to fiddle too much in the winter.

Not sure why there would be a 3 port and 2x2 ports either as that's just pointless too and wouldn't make sense to have both.

I thought something to do with the two cylinders all three are connected to the terminal block in the loft albeit the 2 ports are common so would both open at the same time.

I think you need someone in to go through the whole system and map out exactly what is doing what, so you can get some kind of baseline and from there you can look at what controls may need to be added and how things should be properly configured to give you the control you need

I think so too, thanks for confirming I need to work out a diagram of what it is doing. Might have to grab my SiL on his next visit, don't think Mrs B will be much help.

 

[Stuckinarut]

Yes, industry standard backplate, nothing is needed on 2 as mentioned by @UpgradeME. If you wanted to add a room thermostat the either go wireless or add some cable to wherever it’s being positioned. You can get controls that allow both the programming and room thermostat as one, such as Hive, Wiser, Tado, Honeywell et al.

 

[theboots]

Unsurprisingly I am an idiot, not news to anyone that knows me.

I'd just glanced and marked the pump as a 3 port, it all makes a lot more sense now that I've been and spent an hour or so in the loft making note of the cable colours properly. I seem to have three 2 core cables running to the loft, one is permanent 240v supply, one is from the controller pins 3&4 and the other from the boiler I think this must be the switched supply for the pump.

1 == unused
2 == blue from controller => brown of tank stat
3 == brown from controller => brown of the 2 port for the heating
4 == blue (neutral supply) => blue pump+blue of both 2 ports
5 == blue of tanks stat => brown of 2 port for water
6 == unused
7 == all earths commoned
8 == brown (supply +240v) => grey of both 2 ports
9 == blue (switched neutral from boiler) => orange of both 2 ports
10 == brown (switched live from boiler) => brown of pump

Think my outline plan of interrupting the brown #4 on the controller and putting it through a stat should be doable.

 

[UpgradeME]

To ensure it’s easy for anyone to work on in the future, it’s best to use standards… if you Google S-Plan wiring, when you’re tidying up the loft, (or adding room stat) I would rearrange the connections to match in the wiring center.

As @Stuckinarut mentioned above, I would also look at more modern controls that integrate programming and room stat, especially if for example mobile App control would be useful for you.

 

[Mister Banks]

Yes, industry standard backplate, nothing is needed on 2 as mentioned by @UpgradeME. If you wanted to add a room thermostat the either go wireless or add some cable to wherever it’s being positioned. You can get controls that allow both the programming and room thermostat as one, such as Hive, Wiser, Tado, Honeywell et al.

Wiser and, I think, Tado aren’t combined thermostat/programmers. The other room thermostats are just that and the programming is done via an app. Wiser still functions with no internet but Tado doesn’t.

 

[Stuckinarut]

Wiser and, I think, Tado aren’t combined thermostat/programmers. The other room thermostats are just that and the programming is done via an app. Wiser still functions with no internet but Tado doesn’t.

Apologies, I thought the idea of having a 2 channel Wiser or 2 channel Tado, that control hot water doubled up as a programmer, as surely you could then set timed control for hot water. What other room thermostats?

 

[Mister Banks]

Apologies, I thought the idea of having a 2 channel Wiser or 2 channel Tado, that control hot water doubled up as a programmer, as surely you could then set timed control for hot water. What other room thermostats?

Sorry, finger trouble ignore the word "other".

 

[Mister Banks]

Apologies, I thought the idea of having a 2 channel Wiser or 2 channel Tado, that control hot water doubled up as a programmer, as surely you could then set timed control for hot water. What other room thermostats?

Wiser room thermostats only adjust room temperature. Timer control for HW and CH is all done via an app. I believe Tado is the same.

 

[theboots]

To ensure it’s easy for anyone to work on in the future, it’s best to use standards… if you Google S-Plan wiring, when you’re tidying up the loft, (or adding room stat) I would rearrange the connections to match in the wiring center.

Noted, I think a job for once the heating is no longer required. It was bit chilly this morning and my name would be mud if I made a FUBAR.

As @Stuckinarut mentioned above, I would also look at more modern controls that integrate programming and room stat, especially if for example mobile App control would be useful for you.

I was looking at the Netatmo WiFi stat, my SiL uses their valves. The stat comes with a relay control I could mount near the boiler, break into the 240v on the controller to power it and router the switched live for the 2 port heating valve through it as far as I can see from the S-plan diagram that would effectively electrically be where a wired stat would be, the 2 port energises the pump and the boiler.

 

[UpgradeME]

I’ve been using the Vaillant vSmart for the last few years, which is a rebranded Netatmo but fully integrated to the boiler to give modulation of flow temperatures and weather compensation (the two key things I would look for in any new device).

Vaillant uses eBUS to communicate between controls and boiler, other manufacturers use OpenTherm. If you’re thinking about upgrading, maybe consider the end goal and work backwards? E.g. are you intending to keep the existing boiler or replace in the near future?

I’m a tech person but the last time I looked at WiFi TRVs they were so overpriced I would never be able to recoup their cost so avoided them.

If it were me, I would research if weather compensation and flow modulation can be incorporated into your current system… if not, I would look for something that was opentherm compatible to future proof myself a little.

Note: The flow modulation essentially is the room stat saying “the room is currently 17c, I want it to be 19c, heat the water to Xc as it’s Yc outside” rather than a traditional room thermostat which says “turn on the boiler at whatever temperature it’s set at, I’ll tell you when to turn off” (the former method is a lot more efficient, so saves £’s

 

[theboots]

Vaillant uses eBUS to communicate between controls and boiler, other manufacturers use OpenTherm. If you’re thinking about upgrading, maybe consider the end goal and work backwards? E.g. are you intending to keep the existing boiler or replace in the near future?

The current boiler is a Potter Prima 80F I am unsure exactly how old but it is not modern ( cannot determine anything from the serial#). Google suggests they stopped making them in 1997 if that's the case then it is at least 28 years old. At the moment I am unsure what to do with it. For sure a modern condensing boiler would be more efficient and judging from how much I sprang for the Vaillant at the last place it would be around £2500 to swap out. It obviously doesn’t have weather compensation or any smarts, not even currently a room stat. Gas consumption is hitting maybe 130KW a day right now about double the last house,. Albeit detached bungalow VS traditional semi some will be efficiencies I am sure.

I’m a tech person but the last time I looked at WiFi TRVs they were so overpriced I would never be able to recoup their cost so avoided them.

Thanks. The Kasa ones are IRO of £25ea plus a hub, e.g for the house I'd need to spend IRO £200. The thermostat is going to cost around £140 that will be the first control and might give me enough flexibility without needing to update the existing RWB2 controller too.

If it were me, I would research if weather compensation and flow modulation can be incorporated into your current system… if not, I would look for something that was opentherm compatible to future proof myself a little.

At the moment I am toying with once I've sorted some PV and a battery here maybe swapping the boiler for a ASHP I really need to dig into that more. For sure it looks like buying a boiler after 2035 will be impossible right now and I could get a grant towards ASHP.