Hot water always on when Central Heating is on
Hi
Just had an engineer replace our Drayton LP112 with a Smart Wireless Tado. A day after I realised that the hot water always comes on whenever the CH is turned on, even though the app shows it as being of. The engineer has come back and spent a few hours troubleshooting but has been unable to resolve. He has suggested installing a second motorised valve next to the hot water tank in order to independently control the hot water.
I am not sure this should be necessary as the Drayton was previously able to control the hot water independently. I am therefore wondering if the wiring is wrong but have been reassured it is not.
Any advice is greatly appreciated
Please see photos attached
Answers
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So is your system Y plan, S plan, or gravity hot water?0
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Certainly not gravity fed as no tank and I believe its Y plan (looking at the instructions diagram from Tado).
Thanks for replying0 -
Looking at the spec of the Honeywell 40003916-003, it shows as being a mid-valve (and there is only one) so it should be a Y plan I believe
Just to add there is also a room controller in the hall which has not been decommissioned. I did ask about this but the plumber advised it was not necessary to remove/decommission
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Sounds like a wiring problem, or is the wireless receiver wrongly set up. Presumably you have a wireless temperature sensor somewhere, in which case for tado° to work correctly my understanding is the old room ‘stat should be turned up to full or bridged out. But it’s hard to speculate without seeing the wiring. If yo have a multimeter you might be better able to work out what’s going on. This is a helpful link: https://cdn.brandfolder.io/607DGEMS/as/tqh86npbjjhws5gwkxfncbfh/104172-DIGITAL-WRP01IB01-INSTALLER_MANUAL-TA-UK-00-V2.pdf0
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Thanks hughbilly - will turn up the old stat to full and see if that changes things
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This isounds like a wiring problem or a faulty mid-position valve.
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That's what Tado support are leaning towards. Is there enough information in the pictures above to diagnose? I looked through a lot of previous posts and the closest I could find suggested the black and grey wires should be switched round and earth should be in HW NC ?
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PS - I turned the old stat up to full but that didnt change anything
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I would have a close look at the wiring, if you have, or can get hold of, a multimeter it can make life easier because you can actually buzz the wires out . . .
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In case this helps the diagnostic process. I tried the hot water only this morning, and it fired up the central heating as well (even though the app says it's off). Could this lean more towards a faulty mid valve or still an issue with the wiring.
Many thanks0 -
I think there's an issue with your wiring. from what I've seen of wiring diagrams, Y plan should also have a wire from HW NC to the valve but you have nothing connected there. What is odd is that there doesn't appear to be a spare wire visible. Has the engineer cut it short or tucked it away so it's not visible?
Don't move any wiring yourself. Especially moving earth onto a live terminal!
I'd be getting the engineer back as they've not installed it correctly. I'd also say that was laziness on their part not to remove the old thermostat as it's redundant and the wiring should just be bridged
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Thanks David
Based in the Tado wiring diagram, I agree with you re the HW NC. There is no wire hidden that I can see.0 -
Weird. Looking at the Honeywell 40003916-003 instructions, there should definitely be a connection from HW NC
Time to get your installer back or find another that understands Y-plan
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Further update - had a different plumber look at the set up. the earth wire was not in fact earth (only in colour) and its now connected to the HW NC as advised. The pipes are very hot so its difficult to confirm if everything is all resolved, but it does seem better than previously. CH doesnt come on when the HW is on (as it did before)
One question - the plumber tested the HW wiring to see if it was live when the CH was on but the HW was off, and it did light up the screwdriver (he didnt have a multi meter with him). I think I have read elsewhere that the HW circuit is live when the CH is on, even though the HW will not heat up - would that be correct, can anyone please confirm ?
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The Honeywell mid position valves do output a lower than mains voltage current at certain points in their operation. Although the voltage is too low to fire older boilers it does cause problems with some modern ones and there are mods to overcome this if necessary. There's quite a lot of discussion on the matter online, for example here:
https://www.diynot.com/diy/threads/honeywell-v4073a-orange-wire-staying-live.314159/
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I’ve wasted a lifetime working out what is happening with just one mid-position valve and the control wiring in a rellies home. Best replaced without question; or plumbing and wiring two new S-plan zone valves.
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Have to say, with all due respect, our mid position valve has performed faultlessly for over 20 years and has survived Honeywell, Horstmann, Hive, and finally tadoº control systems. Wired by me with a homemade wiring centre, the operation of the valves, and how it achieves it, does take a bit of thought to understand but there are some good web based resources which explain it pretty well.
In case it's of interest here's my Y plan system wiring . . .
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