combi-boilers and water pressure

[jenb]

Hi All,

Am thinking of upgrading the aged hot water system in my new flat, from a simple boiler and three tanks (hot, cold, header) affair, to a combi-boiler so I can free up the space the tanks are taking up.

My main concern is with water pressure. The mains pressure into the flat (2nd floor - top) appears to be pretty good (in my humble opinion). However the hot water pressure is shocking, resulting in dribbling showers ; I presume this is because the hot water tank sits floor level. There is a pump, but it looks pretty shot.

Am I right in thinking that by putting in a combi-boiler hot water should be supplied to outlets at the same pressure as the incoming mains? Hence I can expect better hot water pressure with this new water system arrangement? = good shower!

Also is there any (simple) way of measuring what the water pressure is? Some of the shower heads I have been looking at say they require 5.0bar minimum, which I think is higher than mains pressure....2-4bar ??? according to the Thames Water website...

Thanks

 

[Bahco]

You will get better pressure with a combi than your present system
Shower heads do not need 5 bar
Have a combi fitted and you will be more than pleased. My shower is fitted to the hot supply from a combi and I need an umbrella when I take a shower

 

[oilman]

Flow rate is more use than pressure in some respects. You can measure this using a bucket and a stopwatch (or even an ordinary watch). 12 litres/min is the minimum you should have for a combi (and at peak demand times, not at 2:00am.

 

[jenb]

excellent - thank you for the numbers - I will test out the flow rate tomorrow.

oh and yes - I had a look again at the shower head pressure requirements - 5.0 bar was the maximum rather than the minimum for the particular model I was looking at! That makes more sense....

 

[vxxbcks]

However the hot water pressure is shocking, resulting in dribbling showers ; I presume this is because the hot water tank sits floor level.

The hot water tank is just a big pipe. The pressure comes from the cold tank in the loft, which presumably isn't far above your shower head.

Have you considered just installing a shower pump for about £100?

 

[jenb]

I see what you mean. Cold water tank is on top of cold water tank, not even in loft, so no wonder the pressure is rubbish!

Could just put in pump, but want to free up the space the cold and hot water tanks are taking up (very large cupboard next to the bathroom).

BTW - measured cold water flow rates from the kitchen tap as oilman suggest - looks like it is ~ 17 litres/min. Good enough for a combi-boiler and then some.

To compare, hot water flow rate out of kitchen tap ~ 4 litres/min!!!

Thanks to everyone who has taken the time to comment. I feel much better equiped to have a sensible conversation with my plumber/corgi man!