Hot Water Only Comes On With Heating

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A friend of mine has recently changed his room stat for a Honeywell DT92E wireless.

Since making the change everything seems OK except that his hot water will only heat when the heating is running.

He has a Danflos EP7155Si programmer.

Can anyone help with a solution (which I am assuming is a simple wiring change in the main wiring centre/junction box)

Thanks
 
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If it worked OK originally, the room stat would have been only wired to and controlling the central heating and not connected to the hot water system at all. So the wires that went to the original room thermostat would simply be rerouted to the new Honeywell DT92E receiver.

Unfortunately where and how the various components are physically wired to each other varies from installation to installation depending upon the layout of the property, if it has been modified at any time, and the preferences of the original installer etc., so without knowing what wires your friend has moved from where, to where and what they were doing before, it's very difficult to diagnose over a forum.

However, if your friend can restore it to its original condition, so that it's working correctly with the original thermostat in place and the hot water functioning on its own. Then, with details of the original thermostat, and details of the wires connected to it, we can advise how to replace it with the Honeywell DT92E.
 
U

undertrained

Like Stem says, unless any major retiring has taken place, the thermostat is only used for heating. Could be coincidence that a valve has failed, is it a 3 port by any chance?
 
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I can't think of a fault with a 3-port valve that would create the problem described by the OP. When the 3-port valve is not powered, it sits at hot water only position, which is where it would go if the motor failed. And when hot water is required, the boiler / pump is controlled by the hot water cylinder thermostat, so I would be more likely to suspect that. It would be very coincidental, although not impossible, if it was working before for something to fail at the exact same time the thermostat was replaced

Of course this all assumes there is a 3-port valve, we haven't been told that.
 
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It may be irrelevant but we had a boiler that had a similar issue: the domestic hot water only worked when the heating was on. If I remember right it was down to a stuck impeller (?) Which meant the system couldn't detect if dhw was on or not.
 
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Methinks you have a combi boiler and not a Y-plan with a 3-port valve, as to its relevance, that depends on the type of system and we don't know, so it's all guess work really. Although the OP mentions a 'wiring centre' and they aren't generally associated with combi boilers.
 
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A friend of mine has recently changed his room stat for a Honeywell DT92E wireless.

Since making the change everything seems OK except that his hot water will only heat when the heating is running.
I had a similar issue with the house I bought. I traced it to the wiring having been modified so that the room thermostat was permanently live. I guess that was done to support a wireless stat they had taken with them. In order to give control back to the main switch, they had wired the heating switched supply to the live side of the motorised valves. So you had to have the heating on to get any power to any of the system - but the room thermostat was always live.
 
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Hi, apologies for the delay in responding. I have passed all the replies onto my friend who is going to check the wiring in the main wiring box and check against the 92DE to see if he can spot the discrepancy.
 
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