Either Hot Water or Radiators for Worcester Greenstar 30cdi, not both at the same time

[Kevinyw]

I recently installed a Nest Thermostat on the Worcester Greenstar 30cdi combo boiler, to replace the Honeywell one. I noticed that when the radiators stop when I turn on hot water (showering). The radiators turned back on 1-2 minutes when I stopped showering. Is that normal? I changed back to the Honeywell a found the same happen. Is that normal?

 

[Why Not Indeed]

Normal for a combi boiler.

 

[helplessowner]

A combi can only heat one thing at a time, which is either the central heating or the water for the hot taps/shower.
The hot water takes precedence, so as soon as a hot tap is turned on the heating is diverted away from the central heating in order to supply hot running water, and when the demand for hot running water stops, the central heating turns back on.

 

[ChrisJP]

It's one of the drawbacks of combi boiler systems which do not have any hot water storage at all and heat water only when it is demanded by someone opening a HW tap. It can also take a long time for the hot water to reach the tap and, if someone else in the house is also demanding hot water, both taps can end up supplying just luke-warm water.
There is a lot to be said for the older open-vented CH & HW systems with a header tank in the loft and a HW storage cylinder. This also gives you a reserve of HW in the event of a power outage and, if the HW cylinder has an immersion heater fitted (which most do) another way of getting hot water in the event of a boiler outage.
What's not to like?

 

[Elkato531]

It's one of the drawbacks of combi boiler systems

In all my years of installing, servicing and maintaining combi boilers, I have never come across anyone who found this to be an issue in real life. Unless you're taking very long showers, I doubt you would even notice the fact that the CH was down for a few minutes. In fact, the most up to date boilers and controls for stored hot water use hot water priority which also diverts heat away from the CH.

 

[Why Not Indeed]

Drawback it may be, but given the space requirements of other types of system, it's one that many seem able to just put up with.

 

[opps]

You may also find that during the summer, after a shower, the nearest rad will get warm as the boiler needs to dump the hot water in the system once the shower finishes.

 

[ericmark]

I seem to remember it is called the W Plan, in my homes in the main a radiator will stay warm for the time one takes a shower for, the exception was the fan assisted radiator.

As to Nest, I fitted because it has the thermostat hard wired to the heat link, so no worry with flat batteries, and I can control CH and DHW from the thermostat. However it claimed it connected to the MiHome Energenie TRV heads, and yes the same program on my phone can control both together, as I lift or lower the wall thermostat temperature the TRV head will also lift and lower to match.

However what I wanted was for the TRV to tell Nest when heat was required, it will not do that, even when setting a schedule on Nest, the TRV will not follow, only when one manually changes temperature with the TRV follow the Nest wall thermostat, which is also the wrong way around.

The USA version has the option of temperature sensors, but they will not work with UK version.

The geofencing you can only set the eco and comfort temperatures, there is no option to set the distance. So rather useless, it had a load of other smart options, like anti legionnaires, I had to turn them all off, and the geofencing caused the house to get cold when the local EE mast was damaged in the wind, so had to turn that off.

The auto working out a schedule relies on all doors always being either open or closed, have door open one day and closed the next and one gets a really weird schedule set up.

Lucky I am not using the OpenTherm option, so I have been able to set up another wall thermostat in parallel, that has cured the problem with Wizer and Nest Gen 3 in parallel, only the Nest does DHW, but considering how Nest worked for me, it could be it is turning off at inappropriate times.

I am sure Nest would well with open plan homes, and hot air systems, but with a 12 room house, with doors on every room, it was a failure. Only good point, it it can be controlled from my PC, and the battery should never go flat.