i have a vokera combi boiler, the cold water pressure is fine but the hot water is very low. I don't know the first thing about boilers, any help would be appreciated. thanks

robbie, April 2009

Hi you may have a furred up hot water heat exchanger this would definately slow the flow down as the lime scale would reduce the bore size for the water to flow through

Allen, July 2009

The flow is controlled by the boiler to maintain the demanded temperature so a high temperature demand may mean the flow is severely cut back, say in winter when the water input is colder. However, if the flow has been good and now it's not this may indicate a component problem. If the boiler is working at all - it ignites, there is hot water in the heating circuit - and the problem is just in the hot water taps then it could be the Feedback Temp Sensor or the Flow Control Valve and these both connect back into the Control Board so several things need checked out.

slapdash, May 2009

There's an aticle about it here...

http://www.diyfaq.org.uk/plumbing/combi.html

Pressure into the boiler depends on the mains pressure - flow rate (volume per unit time) depends on the ability of the boiler to heat the cold incoming water to the required outgoing temperature.

The hot water pressure at the taps is a function of the flow rate (usually lowish with a combi) and the resistance to flow in the pipes - also lowish.

Well, that's how I read it in the article anyway...

Peccavi, April 2009