Best way to get power to a wireless thermostat controller?

[Andy.T]

Hi all,

Sorry, this is probably a bit of a crossover query between electrical and plumbing/central heating. Mods - Please feel free to move it over there if need be.

I have a Tado smart thermostat and it's all installed and working fine for the most part. The only niggle is that it's sited where my old thermostat was (in the hallway) which isn't a very representative place to measure the living area temperature of my house of course. I therefore would love to be able to move the smart thermostat to my lounge. Handily, the thermostat is battery powered and can be made entirely wireless by adding a Tado "Extension kit" into the system.

The Tado Extension kit just replaces the smart thermostat, turning the boiler off an on as required via its signal cable (when the thermostat tells it to). However, unlike the thermostat, the Extension kit needs its own power supply. It comes with a fused (3A) three pin plugged cable that ends in Live and Neutral bare wires.

I got a local electrician round to wire in the Extension kit, I thought it would be as simple as either taking a direct feed from somewhere, or worst case, installing a power socket near to it and using the supplied 3 pin cable.

He was very helpful, but said that the way the boiler and stat are wired currently doesn't really comply with modern regulations. In that it is kind of mixing 230v wiring and low voltage signal wiring within the boiler circuit (and having two different voltages on a single circuit is bad practice apparently?).

He's suggested that the better/safer solution (and neater too since it wouldn't require any extra cabling) would be to change it to be be switched 230v. My boiler (Remeha Avanta Plus 39c) can be wired in a few different ways, but changing it would mean opening the boiler which obviously the electrician isn't certified to do. He said that if a heating engineer changes it to 230v switched live, the three core wire that already runs to the thermostat currently could bring power and the switch signal.

I'd love to know what do you guys think? Does that seem like the best way? Is there any downside to going 230v switched live?

I just want to get a sense of whether it's a job for a heating engineer (as the electrician suggests) or if it would be worth just getting another electrician to have a look.

Let me know if you needs any photos or wiring diagrams for the stat or extension kit, I've got the boiler manual too if the wiring pages from that would help.

Thanks for reading and for any pointers!

Andy

 

[EFLImpudence]

The regulations state that a cable or cables carrying different voltage bands must be insulated to the highest band - e.g. 230V.
So, it depends on the type of cable you have - probably alright if suitable for 230V.
If requiring a change then opening the boiler will be necessary.

This depends on the type of boiler.
If the outer casing IS the combustion chamber then, strictly speaking, you need a gas qualified 'engineer'.
If it is one with just a decorative outer cover then anyone can do it.

 

[Andy.T]

If the outer casing IS the combustion chamber then, strictly speaking, you need a gas qualified 'engineer'.

Thanks so much for that, yes unfortunately on my boiler, the outer cover is the boundary of the sealed combustion chamber.

As you can hopefully see in the attached pic, the wiring as it arrives at the boiler (from the switch in the old airing cupboard) comes from a thick white cable (8mm) into a junction box and then a thick black cable (power I guess) comes out of that into one part of the bottom of the boiler and a pair of thinner (presumably signal cables) goes into another part. So it would need to be a Gas Safe engineer if we go 230v switched, to change things inside the boiler, I guess.

Is it worth going 230v switched do you think? Any downsides to going that route?

Thanks,

 

[ericmark]

I seem to remember the Tado is an "If this then that" (ITTT) device, and is designed to work hand in hand with the eTRV (electronic thermostatic radiator valve) so it does not really matter what room it is in.

The switching on and off of the boiler is last resort, what should happen is the TRV will adjust the water flow and as this reduces the by-pass valve opens so hot water is sent back to the boiler which in turn causes the flame height to reduce, so rather than switching on and off the boiler gradually reduces output meaning a low hysteresis with the temperature.

Although in theory the anti-cycle software of the boiler should take over once the boiler can't reduce flame height any more, in practice this does not really work, so we have a room thermostat to switch the boiler off as summer approaches, in winter we do not need the room thermostat.

This is all well and good if the TRV is set to a single temperature, however when we fit eTRV's then as we change the temperature to a higher level we need to ensure the boiler is running. It actually seems the wrong way around, but the eTRV follows the thermostat so as you lift the temperature on the thermostat so the temperature also goes up on the eTRV so boiler is actually running at temperature change.

The better system as used with the EvoHome is where the thermostat or controller follows the eTRV.

However the point is since the thermostat is only to trigger the boiler when temperature is increased or to shut off the boiler in summer, the location of the thermostat is not really that important.

There is however a problem with wireless thermostats, the cheaper types send a signal when boiler needs starting and stopping, however the receiver does not reply to the sender, so if anything blocks the signal the boiler will remain as it was either getting the house hotter and hotter which is not really a problem as the TRV will take over anyway, or getting the house cooler and cooler, this is a problem. The more expensive models have two way coms so if the signal is blocked it will retry. So although we don't really need the ability to change the temperature of the thermostat on the phone, those with that ability tend to be better quality.

Since we can alter the room temperature with a computer or phone direct to the eTRV there is no point accessing the over all thermostat other then if set to follow changing the over all thermostat will also alter all the eTRV set to follow.

Because any TRV works better than a room thermostat because it integrates with the boiler giving continuous control analogue rather than digital, using a programmable thermostat without also fitting eTRV's is rather pointless except for very old systems pre condensate, or non water systems i.e. hot air.

 

[bernardgreen]

There is however a problem with wireless thermostats, the cheaper types send a signal when boiler needs starting and stopping, however the receiver does not reply to the sender, so if anything blocks the signal the boiler will remain as it was either getting the house hotter and hotter which is not really a problem as the TRV will take over anyway, or getting the house cooler and cooler, this is a problem.

It gets better ( or worse )..... When the modulation fan in the boiler is running the boiler creates a bit of spurious radio frequency energy. Not much gets out of the boiler casing but if the signal from the remote thermostat is weak then the signal to turn OFF may be corrupted or not received. Some service technicians consider that as the ON command was received then the wireless link is working properly.

Some protocols require the thermostat to send the ON command once followed by KEEP ON commands spaced a few minutes apart while the boiler should be burning. If the boiler does not receive the KEEP ON commands then it times out and switches OFF. Repeated ON commands instead of KEEP ON can result in the boiler stopping on time out and then re-starting when it receives the next ON command ( when there is no longer any spurious radio frequency energy from the stationary fan motor ). This can appear to suggest the boiler is cycling ON OFF due to a fault in the boiler and again the wireless link may not considered as suspect.

 

[Andy.T]

Hi both, thanks for that.

The Tado TRVs are actually quite a new item (they've only just been released in the last month or two) but the Tado thermostat itself has been out for a couple of years. The TRVs are an optional extra to the system, they're not required to run it in its simplest form. The Tado thermostat can be used on its own, to just replace a normal thermostat, it adds geolocation based, weather compensated control to what normal thermostat would do.

I'd not been planning to add the TRVs at this stage, it'll start to get expensive quite quickly, and I've been maintaining a healthy degree of scepticism so far.

Picking up on Bernard's point about modulation, I think whilst the Tado thermostat can be configured to control the boiler via modulation, my boiler isn't currently wired to support that, so it's just the simple On/Off you describe, i.e. the same as the old, non-smart, Honeywell it replaced.

I've had the Tado thermostat installed for about 4 months now and so far it's been good as gold really. The only problem I've noticed (which I had before Tado) is when the only one of us at home is one of the kids, they are typically in their bedroom. The heating is therefore on and being thermostatically controlled, but most of the doors are closed, meaning the boiler runs needlessly and it gets fairly warm in the house until the hall eventually reaches a temperature when the Tado turns the boiler off. The non-smart TRVs we have turn each of the rads off but the boiler is still merrily firing up needlessly. This isn't really a limitation of Tado, my old Honeywell non-smart thermostat did the same, it's just that the main thermostat is measuring the temperature in a particularly cold part of the house. I could look at adding the Tado TRVs but it still would mean the boiler was firing up needlessly, just that the boiler was working less hard as warm unused water from the rads is returned as Eric explained.

My thinking of simply moving the thermostat to the lounge is when the above scenario happens Tado will be measuring a far more representative part of the house and will therefore turn the boiler off when a reasonable overall house temperature is reached. I didn't really have the option of easily moving the stat somewhere better before, as my old Honeywell needed a cable running to the boiler.

So I'm pretty set on moving the stat to the lounge, as I think measuring the temperature in the living part of the house makes sense in any case.

Any thoughts on the idea of moving to 230v switched live?

 

[ericmark]

We can only theorise as I have not been in the house long enough to be sure, but the problem is when we are likely to have a warm day we would like the thermostat not to start the boiler, to do that the thermostat needs to be set on the low side, our weather will never be warm enough to get any part of the house at say 18°C in the morning, however a couple of degrees less and it might, so having a hall thermostat set at 16°C or 17°C would still allow the central heating to warm other rooms to 18 ~ 19°C in the winter, but would shut off the boiler in the summer when your likely to get a warm day. So I would leave the thermostat where it is and set it a degree or two lower than what you want the rooms.

What I have found is the standard TRV is not that accurate, the bedroom will get warmer and cooler when the hall thermostat is altered, however now the eTRV are working correctly, the two rooms where they are fitted are spot on.

The question is if it is worth having eTRV's which can be linked to phone or PC? In the main to link to phone or PC you need a hub, plus the eTRV costs about £7 more each, but just like the room thermostats we don't know the quality, the MiHome I have so I know these have two temperature sensors one for air and one for water and so auto compensate for the heat from the radiator, these stand alone heads are likely the cheapest eTRV heads you can get, £22.51 compared with £36.50 I paid is quite a saving, specially when you include price of hub not required with the cheaper valves, but I can't find out if the cheaper valve has double temperature sensors so don't know if they will work as well as mine.

To be frank I rarely alter the settings, when mother goes to rest bite I may turn off her room, but for the few times I do that the extra cost is not really on. However if you want to alter on a regular basis then maybe extra cost is justified. But I in first few weeks experimented to find warm up time for room, so how much in advance of wanting extra heat I need to turn up the eTRV but once set they simply sit there without altering them.

What I found really annoying was lack of instructions with the heads, I had to hunt out the instructions on line, by time I had found them I had already fitted the head, only to find I had fitted the wrong spacer, the procedure to match the valve to head was not easiest with one push button and one tricolour LED counting how many flashes of what colour and having to remove and refit batteries etc was not the easiest set-up.

What I want to do is fit a TRV to the hall radiator, but this then means I need to think hard as to where to fit the master thermostat, likely still the hall, but set higher than the radiator is set.