What happened to my shower?

[Ltnman]

Two years ago we had a 42kw Worcester Greenstar CDi combi fitted. Up until now we have never had a shower and ran the bath at the same time until Sunday. The result was a nightmare!!! I was all covered in soap when my daughter started to run the bath. As a result of her actions I didn’t get a drop of hot or cold water until my screams were heard for her to turn off the taps to the bath.

Normally we have superb water pressure and my water camel shower head gives me a massive soaking so what happened? I was still getting water through the taps in the wash basin when I tried them to see what was going on, though at a much lower water pressure, so it would appear it was only the shower that was affected. The shower is standard and is not an electric variety.

 

[stem]

Combi's have a maximum supply based on the capacity of the boiler and the maximum supply of water available from the mains. Of course this supply falls off if cold water taps elsewhere are running

When bath taps are turned on, the majority of the mains water would take the easy route through them, especially if both were open simultaneously, than via a higher resistance shower.

Shower mixers often have a safety mechanism inside that shut the shower down in the event of a major pressure drop to prevent you being doused with hot or cold water. So it sounds like this operated.

You have discovered one of the weaknesses of a combi. A traditional system with hot water cylinder gives some extra capacity as there is not only the mains flow for the cold, but the hot cylinder has a storage tank feeding it as well, which can help buffer periods of high demand.

 

[Ltnman]

Thanks for the info. So the claims by manufactures that their high wattage models are fine for simultaneous bath and shower usage is just so much hot water, or in my case no water.