Replacing old relay box on combination boiler with two pumps and then integrate Tado controller
OK. The charity's building is run by three boilers. The largest is an old Thermecon s190/240 64kw (yes really) oil fired boiler - the centre of my puzzle.
About 1x1x2 metres in size, it has a large heat exchange unit with two 40mm brass pipe loops running through it, converted on leaving to 28mm piping.
- one handling the supply to a 300L hot water tank feeding the bathrooms and 3 kitchen sinks
- the other handling central heating to 8 large bedrooms each with its own bathroom.
Each loops have dedicated pumps operating on a differential pressure basis. The system is wired with 240v relays in a box (about 12x12x10"). There are no bypass valves, no electro-mechanical zone valves. The box seems to register (via the HW tank) whether there is a need for HW demand and turn off the HW circulation pump. The CH pump seems to be driven by a somewhat wasteful room thermostat on the ground floor. When both pumps turned off, the boiler is turned off. Not really complicated. There may be a pump overrun involved - cant seem to work it out yet.
Rolled over that, a basic Nest controller is in place acting as though it is handling an S plan system. It isnt really but I can see why that logic is applied.
In the last year have saved money by fitting Tado rad stats to each radiator (without any internet interface) and am now at the point where am considering swapping out the Nest controller- but before I do, am seriously considering replacing the relay box.
Does anybody here have suggestions on:
a) what the replacement might be
b) the wiring
Am even wondering whether I should consider using a UFH wiring centre to keep it simple and marry that with a Tado controller. I know this isnt a complete picture but your reflections may help me complete the required logic.
Suggestions?
Comments
-
@policywonk Hello Policywonk. Some 'in-principle' suggestions …
a) If it's working, what are the reasons to swap out the relay box for a UFH wiring centre? For a typical non-combi boiler, S-Plan CH and HW, the most likely choice is the Tado wireless starter kit. This kit gives you an internet dongle, wireless room stat, and the wireless receiver as the 'zone controller' (by relay) for the CH and HW wiring. Obviously, you'll need a reliable internet connection. If you need stand-alone schedules, best to check with Tado if they are (or will be) supported in your region.
b) BTW, I took a brief look at the Nest documentation (page 10) to compare with the Wireless receiver.
The wiring looks straightforward? N > N. L > L. 1 > CH NC. 2 > CH COM. 3 > CH NO. 4 > HW NC. 5 > HW COM. 6 > HW NO. Earth > Earth. The starter kit includes wire links and Wago connectors to use where needed.
The known unknown is device range, especially as the Nest thermostat says it's range is 30 metre. You'll have read that some Tado users, (usually in 'larger' homes or older homes with thick walls) may have range connection issues between the internet dongle and some distant devices. IIRC, 6LoWPan operates over IEEE 802.15. The 802.15 standard is designed for low-power IOT devices and provides for approximately 10 metre range. If your charity building fits the 'larger' home category, I'd be wary of the V3+ dongle to device 'range'.
Tado have indicated that the 'X' range will be launched for the UK in autumn. That may negate some of the above concerns.
I'd suggest that you reach out to Tado support for their advice. There is a 'chat' function on the main Tado web site.
HTH.
0 -
Hi.
Why remove the relay box? Two reasons.
(1) In the last four months I've had to replace four of the six relays and it does keep presenting problems with reliability.
(2) Still dont know why it has six! I suspect the stuff in that box has been there since the 1960s. I havent yet gone through its wiring to work out its entire logic. In the end there is ONE boiler, and ONE CH feed, ONE HW feed - and my view is that if I could spare two days I'd rather replace it with something that I know is stable, reliable.
Why a UFH wiring unit? Purely an idea - as it has built in relays, so the logic of application is simple. And although there is only one CH heating zone, it would be simple to understand. It is OTT, but if there is something else on the market which would perform a similar job, with solid state relays, or if someone has a wiring diagram I could apply - I'd prefer that. Dont mind building my own circuit board.
The Nest? Dont worry about that. Pretty sure I can swap it with a V3+ full starter kit. My primary concern is to replace that box, given that it has broken down so many times. Dont want to install two port valves, when good relays would be more reliable in the long term.
I know this sounds a bit hairbrained. It really isn;t. Ideas would be welcomed.
0 -
@policywonk Thanks for the explanation. Thinking aloud about the relay box … could an 'off-the-shelf' S-Plan relay system simply be a couple of the motorised heads for zone valves and a wiring centre?
0 -
Was trying to avoid motorised anything to drive the pumps because they at, in my experience, unreliable over five years. Hence looking for a solid state relay based box.
Then, thinking out loud, surely this isn't the first time this need has arisen?0 -
@policywonk I've not had much luck with solid state relays. Had to replace two failed immersion-heater timers for a rellie. The original failure was circa two years old. The first replacement failed after 13 months, just outside the warranty period. The second replacement is two years old and still working (🤞fingers crossed).
Maybe this 16A Salus relay would meet your needs?
0 -
I'll definitely look at this. Thanks @wateroakley
0
