Hot and cold water flow rates not equal?

10 Nov 2009
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United Kingdom

I have recently moved into a new flat which has a worcester 24cdi combi (i think that's the correct model) and the hot water flow is terrible.

I used a bucket to measure the cold water flow rate and the hot water flow rate and got the following:

Cold: 8.5l/min
Hot: 3.2 l/min

I was under the impression that the hot water flow rate should equal the cold water flow rate on a combi system?

Also another issue i have with the hot water is that the temperature fluctuates greatly - if i have the temp on the boiler set high, then it fluctuates from very hot to completely cold, and if i set the temp on the boiler to the lowest it fluctuates from lukewarm to hot (flow seems constant).

Any ideas on what the issue is? I got BG round to have a look and they replaced an incoming valve and it didn't make any difference. The guy blamed the problems on poor water pressure, which i thought wasn't right?

Thanks for any help,

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scaled up or blocked pipework is the most likely
there is a filter in the diverter valve cold water inlet this gets clogged with any grit from the cold main, did he swear a lot whilst there if he didn't then he didn't clean it out (its a pig to get to!!!)
Thanks for the info - is there any way to remedy scaled up pipes? Wouldn't scale affect cold water flow rate as well though? Any other ideas as to what it could be?

The guy did say something about a filter - not sure if it was that one - will have a check on the paperwork to see if he wrote it down. There was a valve that he thought was not opening all the way, and he had to strip the bolier down completely to get to it.

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