Another Hive instalation question..(horstmann 425 coronet)

14 Apr 2009
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United Kingdom
hi guys..just picked up a hive active heating thermostat (for combi boilers).
I currently have a horstmann 425 coronet with a downstairs wall mounted thermostat
and a vaillant ecotec plus combi boiler.
As it is a combi boiler ,i thought to wire the hive thermostat it would just be L N E and CH ON..
but there appears to be a HW on as well.
I have attached a pic of the Horstmann wiring and it is as follows...
boiler - 5 wires L N E grey (pin 4) black (pin1)
stat - 4 wires E brown(pin 5) black (N) grey (pin 1)
feed from isolator switch - 3 wires L N E

the downstairs wall mounted thermostat was just going to be disconnected.
Can someone please have a quick look and advise..
Last edited:
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Are you sure you have a combi boiler? There looks to be too many wires there and a 425 Diadem is designed for system and heat only boilers
Hi Muggles, thanks for the reply.Its a vaillant ecotec plus boiler,had it installed about 8yrs ago to replace a back boiler and hot water tank system.There is no control or timer for the water, just the heating.
heres a pic of the boiler if it helps..
I looked for Instructions maybe I have wrong ones? However it seems there are two types of thermostat 24 volt and connected to eBUS the Hive for single zone does have volt free, but duel zone does not. And if you can use a modulating thermostat then it would seem pointless fitting an on/off type.
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would i be better off getting an engineer to take a look before trying to fit it myself ? I thought it would be pretty straight forward after reading all the threads on here.
Its the extra wire from the boiler thats throwing me.
Your boiler's G10 burner gasket is out of date - they have a maximum 5 year working life. Time for a service

Oh and yes you're right, it is a combi boiler. You'd be surprised how many people get this wrong though!

You could ask your boiler servicing chap to fit your Hive at the same time as servicing your boiler
cheers for gets serviced every Jan, so ill be sure to mention it to them when they come out.
Any advice on the wiring of the hive especially the wires in pins 1 and 4 from the boiler...?
Sorry...put wrong name of timer/programmer. its a horstmann 425 coronet not a horstmann 425 Diadem as originally stated. Main post has been amended.
Anyone got any advice on the wiring ?
Hi Muggles,thanks again for your help....i got all that so far..its the grey wire from the boiler flex that is confusing me (that currently goes to pin 4 of the hortsmann).
Sorry, small screen and I missed that! Corrected version here...

OK the cable you've identified as going to your thermostat can be cut back and made safe. You won't be needing that for Hive.

Your Feed From Isolator Switch flex goes to Live, Neutral, and Earth, as do the brown, blue, and g/y cores from the boiler flex.

Boiler flex black goes to Hive Terminal 3

Boiler flex grey goes to Hive Terminal 1

Do not link Hive L to 1

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