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Old 1st March 2019, 12:52 PM
HPsauce HPsauce is offline
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Default Advice wanted on improving boiler controls

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

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?
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Last edited by HPsauce; 3rd March 2019 at 01:18 PM. Reason: Add a little more detail
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Old 3rd March 2019, 12:19 PM
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IT IT is offline
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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....
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Old 3rd March 2019, 01:17 PM
HPsauce HPsauce is offline
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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.
Quote:
Originally Posted by HPsauce View Post
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.)
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!
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.
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Finally: gone, but not forgotten.....
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e.g. Cruise control, NavPlus/TV, Bose, GSM, Xenons, Solar roof, Parking sensors, Alcantara/leather everywhere of course. (internal dimming mirror added later)
1998 (very early) Ford Focus 1.8 Zetec; ABS/TCS, Heated screen/mirrors, Aircon, Auto-dim mirror, Leather, Trip computer, Cruise control, OEM Ford SatNav with CD changer.

Last edited by HPsauce; 3rd March 2019 at 05:15 PM.
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  #4  
Old 12th March 2019, 11:31 AM
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roberto roberto is offline
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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 ?
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Last edited by roberto; 12th March 2019 at 11:37 AM.
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Old 12th March 2019, 11:57 AM
HPsauce HPsauce is offline
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Quote:
Originally Posted by roberto View Post
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.
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2016 Volvo V40 T5 Cross Country (4WD) with ALL the toys including adaptive cruise etc. etc. Osmium Grey with Blonde/Charcoal leather interior. Polestar performance "optimisation". (A much rarer model than a D2 S8 by the way!)
Finally: gone, but not forgotten.....
1998 D2 PF S8. AgateGrey/Platinum. Every option (I think) except electric rear seats, tiptronic steering wheel, ski hatch, towbar & dimming door mirrors.
e.g. Cruise control, NavPlus/TV, Bose, GSM, Xenons, Solar roof, Parking sensors, Alcantara/leather everywhere of course. (internal dimming mirror added later)
1998 (very early) Ford Focus 1.8 Zetec; ABS/TCS, Heated screen/mirrors, Aircon, Auto-dim mirror, Leather, Trip computer, Cruise control, OEM Ford SatNav with CD changer.
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