Hit water issues after tado TrVs

I have a tado system with an extension for my hot water which is in a cylinder. Had it a few years and all works fine. I have hot water on for 40mins a day and that’s enough to keep it hot. The extension is linked to the tado thermostat which controls my upstairs system.

Last week I purchased a load of tado TRVs and since then my hot water is hit or miss.

Sometimes I have hot water sometime times I don’t.

My theory is that the call for hot water turning on is not resulting in a trigger to the boiler. I think when I do have hot water it’s a coincidence that it’s at the same time that the main bedroom is calling for heat or perhaps another radiator upstairs.

No idea why this would now be a issue?


  • Sorry about resurrecting a dormant post, but this is exactly what I've had for some time (years) and I still haven't managed to get a proper resolution. Every year we get close to throwing this out - if Hive would implement automatic geofencing the decision would be made already.

    I worked out this happens when the TRVs are only calling for partial load because the room temperatures are close to the set point so they don't need to run at full blast.

    In the situation where the heating is calling for partial load, but there is also hot water demand, I expect the boiler to provide whatever load is necessary to maintain the higher flow temperature to charge the DHW cylinder. What I actually see is that the boiler target flow temperature is set down to around 40 degrees by Tado.

    Based on these observations I believe this is what is happening:

    * Imagine my DHW cylinder has been sat for some time and is maybe now at 45 degrees instead of its target 60, and the heating is on but all the rooms are close to their set point so none of the TRVs is calling for full load

    * In this situation the cylinder thermostat will be triggering hot water demand and the 3-way valve will be in the mid-position to also meet the heating demand.

    * The boiler will run, but because of the Tado/TRV issue it will only run at partial load and with a target flow temp of 40 degrees.

    * Water in the circuit will be pumped round and will actually be heated in the DHW coil because the tank is already hotter than 45.

    * The boiler shuts off as the target temp is reached very quickly, then constantly cycles as it realises it's still getting demand. The anti-cycling protections kick in, but this doesn't help the problem that it's not heating my hot water.

    I find this happens around Autumn and Spring, when temperatures outside are not cold enough to have a high heating demand. In cold periods the demand is high enough that the boiler is running at full load often enough to recharge the hot water easily.

    Things I've tried to fix it:

    * Manually turn the temperature up high in a single room to trigger full heating demand. Works but needs doing every time.

    * Turn the heating off and allow the system to work on satisfying just the water demand, then turn heating back on later. Works but needs doing every time.

    * Set the boiler to DHW priority. Works, but means we have no heating at all if the water needs filling. I've woken to a very cold house on a couple of occasions when I tried this, if someone had used all the hot water late the night before.

    * Set smart schedules so that hot water and heating don't overlap. Works, but makes managing schedules a pain and is really just a manual variation on the previous fix. Doesn't work so well in the winter when people want heating and hot showers at random points in the day.

  • @matt_t
    This sounds like a job for @GrilledCheese2 as your situation seems really complicated.....over to you Mr Cheese 🤞🙏👍😎
  • It shouldn't really be that complicated:

    * Vaillant eBus boiler, VR65 control centre

    * Tado extension kit

    * Lots of TRVs

    * Would like DHW to work at the same time as CH!

    But any and all help would be greatly appreciated. While I don't mind the occasional cool shower, other members of the household have different views and are quite forthright in making them known 😯