Advice wanted on improving boiler controls
 

I'm sure the combined brain power here can help with this. :D

We have a fairly old gas boiler with an integrated mechanical 24-hr timer and switches that control heating and hot water patterns.
This started to fail ages ago so I replaced (bypassed) it with an external 7-day electronic programmer (Drayton Tempus 7, no longer sold); wiring it in was a pretty simple bit of logic.

The system is an old single-pipe circuit to the radiators and gravity-fed (i.e. convection) to the hot water tank.
There is a tank thermostat (added by me) and wired wall thermostat that is in a bad location (due to later changes in the house that expose it to unusual heat and cold).

I want to relocate the wall thermostat and thought that a wireless unit would be an improvement. So far, so good, plenty of choice there and many/most are programmable too.

But the 7-day programmer for the heating and hot water is also a bit dodgy, the LCD display is fading away making programming more guesswork than anything else.
Again, I can replace the programmer with newer models for a modest sum, £30-£40 seems to cover a good choice and there are plenty that say they are suitable for gravity systems.

Then I thought, we're doubling up on the programming here, why not just get a modern integrated unit with a base wired to the boiler and wireless controller/sensor where it's convenient. Maybe even remote access for when we're away?

That's when it all got a bit messy, the suppliers (I decide to start with Drayton for simplicity) when asked said that the integrated systems are ONLY for fully-pumped systems. Something I actually can't see the logic of.

This is not a multi-zone system so the wiring for the controller is dead simple; power supply and two 2-wire circuits (heating and hot water) that are closed for on and open for off. They all (compatible and allegedly incompatible types) fit on standard baseplates with just those connections. (The current controller is already on such a baseplate.)
Edit: Actually a bit simpler than that as the neutrals are all common. I've checked the original wiring, current controller wiring and potential replacements and all use the exact same pattern of two terminals (hot water and heating) that are made live (mains 240v AC) to turn that function on. Controllers are all double-insulated so only need 4 wires - Live, Neutral, Water, Heating.

The ONLY potential problem I can see is that one "could" logically program the central heating pump to start without the boiler firing up. Our current controller has an installation option for gravity-fed that simply ensures that when the heating is turned on the hot water comes on too.

Am I being logical here, or are there hidden complexities that I'm unaware of?

As far as I'm concerned I could install a modern "all-singing, all-dancing" controller with wireless and remote access and all I would need to do would be to apply a bit of thought to the programming to ensure hot water was on when the heating was on.

Even that wouldn't be really needed, it would be a doddle to fit a relay inside the boiler wiring box that just turned it on when the pump was energised.
(Edit: Having studied the wiring diagrams I don't even need to do that, it's just a matter of rerouting a cable that takes voltage from the pump supply to trigger the boiler so that it will bypass the tank thermostat. CORRECTION, this would energise the pump when only heating water, so a relay is needed.)

Thoughts folks?

Yes,

Its all pretty simple.

In your case you need 3 relay outputs, 1 for the pump, 1 for ho****er, and 1 for heating. Your two inputs are time and the output status of the themostat.

The pump should run when only 1 of the other 2 are active.

I multizoned my house some years back, and run everything off digital temperature sensors (fed into a PC via RS232) and basic logic operates a bunch of output relays (also controlled by RS232). Its old school, but very reliable and easy to debug.

Thats an extreme solution for a single zone house, but all you need is some basic timing and themostat live or not logic by the sounds of it....

Thanks Ian, useful input. +++
However, as I already have all the basic wiring in place I'll probably just install a commercial unit anyway. I rather fancy a relocatable wireless thermostat and the potential of remote control.
My last comment (in bold) is wrong as connecting the pump supply to the boiler will of course ensure the pump is energised when the boiler is firing but ONLY the hot water is intended to be on! :o
But I would also need a relay to make it failproof against bad programming.
Logically, as noted by Ian, you need the boiler firing when either or both of heating and hot water require heat input (as dictated by the respective thermostats). Electrically that does really need a relay to do simply.

Edit: The current wiring (which follows exactly the diagrams in the boiler manual) effectively uses the Cylinder thermostat as a switch feeding power to the boiler from either the hot water signal (cold tank) or central heating pump supply (hot tank) so will work fine even without a relay if programmed appropriately. :cool:

slung my wireless thermostat sick of it loosing signal
got shut of the lot and fitted a new modern combi
1 wired thermostat and instant hot water
fit some oversized 2K rads
mine is awesome now
why wouldn't you ?

It's a long story, but basically it would involve massive surgery to our (largish) house that we just don't want at present.

Just realised that I never wrapped this one up and thanked people for their input! So thanks folks and this is what I did:
In the end (late 2019) I bought a Drayton Wiser system, not least because there was a very good discount on offer via Amazon and we had Prime (free) at the time - pre-Xmas buying spree. :tuttut:

Strangely the existing Drayton backplate didn't actually fit the new controller, subtle differences that I don't understand the reason for. But swapping it for the new one (in the box) was a 2-minute job as the wiring was identical.
I've actually mounted the original backplate on a small piece of wood with a mains lead and have the old controller sitting in a quiet corner powered up and ticking over as emergency backup that can be installed in minutes.

It works fine and I've programmed it so that hot water is always on when heating may be required. That also requires disabling some of the cleverer/predictive options in the management but I don't want them anyway.
It gets information on the weather forecasts and seems to interpret that reasonably well to manage the heating more effectively than our simple wall thermostat ever did.
I don't know if we actually save money, but we don't get the "overshoots" that the old system used to produce with hot radiators continuing to warm the house up long after the thermostat said it was at the target temperature. The downside is that it can sometimes seem to take longer to warm up (than it used to) as it's managing the heat input to reach a target, but then I can always easily raise the target temporarily.....

And locating the (wireless) thermostat in a sheltered corner (well away from radiators and draughts) of our lounge works so much better than in the hallway next to the kitchen door with the oven behind the wall!

There's also remote access via an iPhone App so we can turn it back up when about to return from being away - at least that facility is there but I don't seem to have had much use for it...….. :rolleyes:

Interesting stuff Andrew - I'm currently exploring options for our sealed system with x2 heating zones and hot water. The Nest and Hive options look to be non-starters for us (not big Google users in terms of IOT devices) so Honeywell Evohome option is looking favourable, as is the Drayton Wiser you mention :D

I have the Honeywell Evo home system. 12 radiators and a large sealed hot water tank.

Fully WiFi controlled. Link into Alexa for voice automation.
Each room has a set temperature with as many on and off points as you need.
Boiler only comes on when there is demand and I can limit the times when it does come on.
I'm on LPG and have reduced my bills by 50% (£600 pa).
Recovered expenditure in 18 months. Got rid of the bulk tank and now use two large cylinders which are more discrete. It's a DIY fit.
Control it from my phone mostly. 😄

Another vote for evohome for me, my house is zone valve and manifold controlled for the under floor heating, the wiring was fun but logical and worked first time! I have non of their TRVs, so can't comment on those, but overall the system is great.

http://forum.a8parts.co.uk/attachmen...1&d=1613592587

One limitation I found was only one hot water zone per evohome controller, but was able to get creative with that! The evohome software was fairly static for a while, but recently they have made a lot of improvements, I think I'm on a beta programme still but the integration is much better, I use IFTTT to integrate into the home alarm etc..