A friend has a BG combi boiler, at least 10 years old.
When you just turn the hot on you get a good powerful flow of hot water.
However when you turn the cold on you get a powerful flow from the cold tap but the hot dies down to a very weak flow.
I would have expected that the flow from both taps should be roughly equal with a bit less from the hot because of the constriction due to the heat exchanger on the boiler. However I wouldn't have expected such a marked difference.
The major effect of this is that if a cold tap is turned on whilst a shower mixer is on the shower goes cold. With a thermostatic mixer I would assume that the flow would slow down a great deal.
In the past she fitted an electric shower because this didn't suffer from the 'cold tap syndrome' in the same way.
Unfortunately I can't test the exact same set up at home because all our taps are mixer taps so I can't be sure that I am ever getting 100% hot however as far as I can tell our system doesn't do this.
[Mind you I went to a lot of trouble to design the pipework so that the combi got the best possible cold mains supply.]Anyway, it doesn't seem right.
Is this a known problem with combi systems?
I will check where possible for simple things like a valve partially shut somewhere in the mains supply to the combi, but failing that what might be the best way to improve the hot and cold balance?
I guess it depends on where the feed for the boiler splits off from the cold mains.
If it is near the stop c*ck then I assume some kind of flow restrictor could be installed for the cold side.
If the cold supply to the combi is at the furthest end of the cold run then I assume that some kind of in line tap would need to be fitted to the cold feed to each set of taps so that the cold could be limited at each tap. Isolation valves would presumably do this, and probably not be a bad thing anyway.
The alternative might be to run in a new 22mm cold feed to the boiler from as close to the stop c*ck as possible. However major excavations under the kitchen may not be flavour of the month.
The house is being refurbished prior to rental so now is the time to fix anything major before new carpets and stuff go down and tenants are in.
Suggestions welcome :-)
Cheers
Dave R