Worcester Combi - Hot Water and Low Flow

[RealPolitik]

Having hot water problems with a 2-year-old Worcester-Bosch combi boiler - the hot water starts fine, but almost always goes cold after a minute or two. Sometimes it will run hot again of its own accord after a minute or so, usually you have to turn off and on.

It's a bigger problem when running the bath or shower than the basin tap.

The system had a cleaner put through it when the boiler went in and has a MagnaClean fitted, so I'm hoping it won't be a blocked heat exchanger.

Whilst the water pressure is good (about 3 bar), the flow is poor (about 5 l/m) - is that likely to be low enough to cause a problem for the boiler?

 

[John506]

Has it always been like this or just started recently?

 

[RealPolitik]

Hasn't always done it, but the water flow in the property appears to have dropped since it was installed.

I know that low pressure is an issue with combis, but how low does flow need to be to cause a problem?