Worcester Bosch combi - HW suddenly runs cold for a few seconds

[Jez Cunningham]

Hi - I've searched the existing threads but not found an answer...

I've just had a new W-B combi installed and it's excellent. But the question is about what's "normal".

My wife and I both take a shower each morning, one after the other, and the shower is turned off for 10-15 seconds while we change places. After the second person has been showering for perhaps a minute it is interrupted by running fully cold for about 5 seconds.
I quizzed the installer (Accredited WB installer) and he recommended not using the ECO mode. He says the ECO mode (which basically disables pre-heating of the hw heat exchanger) includes a flush of the heat exchanger with cold when the hot is turned off. It's conceivable that it takes a minute to get through the pipes to the shower. So I did as recommended and it seemed ok for several days but today we (I) suffered the cold flush again.
No other taps are used during the showering. It's a Grohe thermostatic shower which otherwise works brilliantly. If we leave the shower running during the switchover there's no problem - except water showering out of the cubicle door.

What is "normal"?
Thanks

 

[ShaunCorbs]

Yes normal it’s the lag of when you turn the shower off and on again it doesn’t produce hot water instantly so either turn eco off or leave the shower running if it’s for 5-10 seconds eg when swapping

 

[Jez Cunningham]

Yes normal it’s the lag of when you turn the shower off and on again it doesn’t produce hot water instantly so either turn eco off or leave the shower running if it’s for 5-10 seconds eg when swapping

Thanks. I've turned off ECO and was disappointed the problem was still there, but if it's normal...

 

[ShaunCorbs]

Thanks. I've turned off ECO and was disappointed the problem was still there, but if it's normal...

Yes best to either leave the shower running or turn it off for 5 mins plus etc