hot water turns on the end of cycle
Hi, what could be a solution here?
Issue: in the hot water schedule the water is heated normally. When time reaches end of schedule, the hot water turns on again for a few seconds. Why? What could be the solution here?
Example: schedule is between 9:30-10:00 PM. Boiler starts up 9:30 and heats until like 9:42, when the requested temperature is reached. Boiler stops heating. Boiler starts heating at exactly 10:00 PM for ~5 seconds and stops again.
Hardware: V3+ (bridge, receiver, wireless thermostat, Baxi duo-tec compact E1.24)
Comments
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@soft_fins Hello, welcome. The fault description is a strange operation. The first question in my mind is whether the lights on the Tado wireless receiver show the HW calling for heat at 10:00pm or not? Second, is this a combi boiler or system boiler and S-plan controls or ? Is this a relay connection or ?
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This is presumably a system boiler as you have programmed DHW (combo being demand).
It might be pump overrun, in which case, it's normal. The boiler is dissipating the heat from the exchanger after running at full tilt to heat water. However, if it's always at exactly 10pm and always for exactly 5 seconds, that may not be the case, as I'd expect the boiler to switch on overrun depending on current conditions, which will vary from day to day - some days it takes longer to heat the cylinder, so the exchanger gets hotter and therefore overrun may be several times at random intervals. Ours kicks in whenever the exchanger exceeds 80C and runs the water around the primaries until it drops back below that level. If it creeps up again, it runs again.
Did this only start after installing tado?
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Hi, thanks for the replies.
@wateroakley: No, no change in the lights on the Tado receiver. It is an S-plan. Tado is connected with OT, not relay.
@DM932187: No, it is not a pump overrun, because the fire is also turning on for 5 sec and real water heating happens. I noticed after some months after installing Tado but I think it worked like this from the beginning. Before that I used Baxi thermostat and also a 3rd party relay stuff. None of those produced this behavior.
I think the following happens: at 10 PM Tado checks if the boiler is still running and if it is then it instructs it to stop the HW. But when it isn't - which is the most case - then this checking somehow triggers the HW production. Or the OT connection at this point stops for a few seconds as if I removed the OT cables and the boiler becomes temporarily factory 'dumb' and starts producing water according to its factory behavior. Tado guys said for my ticket that there is no issues found on their side.
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@soft_fins I'm not familiar with the OT wiring set up as my boiler has WC so I'm on S plan with relay. How does the DHW work in your set up - relay with cylinder stat or is tado controlling the water temp? If the former, I'd expect the call for DHW to simply be on (valve energised) for the half hour and then the cylinder stat to cut that call to the boiler when satisfied (so no tado 'check' at 10pm - just no more power to the valve). So from what you say, somewhere in your set up, you get a new call for DHW at 10pm and this was possibly pre-tado? What was your pre-tado set up?
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@DM932187 I'm not sure if my setup falls into your categories: I have a 130l external dhw tank with water temp sensor connected to the boiler. So the boiler can see the temp always. However Tado cannot - at least nowhere in the app is this data visible. Tado schedules only the 'open windows' and the target dhw value. The boiler pays attention on dhw temp if the hot water window is active. But I think Tado cannot read from the boiler if the temp is reached and even if the boiler is on or off for hot water production. Those functions are visible for heating.
The faulty behavior wasn't present before when I used a Baxi thermostat.
Yes, you're right, something triggers the hot water - or, the connection is lost for a short time, which also causes dhw production.
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