Hot water goes cold as flow increases

[johnnetplus]

I have an Worcester 28i boiler (16months old) and in the bathroom upstairs when I put on the hot water it doesn't get very hot unless I turn the tap to be about a quarter turn rather than fully open. It seems that somehow the pressure once increased (by me opening up the tap fully) stops / reduces the hot water to flow freely. So I end up running a bath for hours instead of minutes!! The CH system seems okay. Yes did lose some pressure in the CH system a few months ago - but once I added more water to the system is seems stable...famous last words!!

I also suspect that the water pressure coming into the house may be set too high (we had some building work done and the builders messed about with the water suppy) - as I hear a banging noise should I quickly turn the cold water tap fully open and then off. Should I go outside the house and turn the water pressure key a quarter of a turn to eliminate this?

Any help from anyone would be good.

 

[ChrisR]

Boiler - may be faulty or may just be a combi....
Get the flow at showering temperature, and measure the flow with say a 9 litre bucket to get a flow in litres per minute. Should be about 8.

Mains - it ISN'T a pressure reducing key, it's a stop cock! It will only affect the flow, not the pressure. If you have really high pressure though, turning it down a bit may solve your banging problem and still leave you enough flow, so worth a try.

 

[johnnetplus]

Yes it's a combi.

Take your point about the outside tap being a stop cock! As you can see I'm not a plumber. Isn't terminology wonderful!

I don't have a 9 litre bucket. I suppose i could get a one litre and time the whole operation X 9 times.

What would the outcome be once I do this? What is the purpose of doing that? Is it to gauge the flow of the water through the system? Unsure - hence my question.

thanks again for your help.

 

[DP]

Any one taking bets on this one?

I say the gas line is undersize.

 

[scatmanjohn]

Did it used to be ok or has it just got gradually worse.

If its always been like that then DP could well be right.

If its gradually got worse then it could well be the gas injectors getting blocked (had a worcester 28i doing this the other week..had me scratching my head until i gas rated it..)
Not a diy job.

 

[johnnetplus]

I think it has always been doing that. As I say the boiler was installed about 16 months ago. The shower above the bath is fine very hot. The hot water from the bathroom sink seems to be fine as well. It's just the bath's hot water tap!

Still uncertain why by turning open the tap fully it reduces the hot water? What is a 'gas line'? Wouldn't I be getting the same problem throughout the house if it is one problem area?