Combi Boiler Hot Water Pressure Prob

tollanarama

Hi,

I've had help from this forum previously & I need help again!!!

I've just moved into a great house with combi boiler for HW & CH.
All works OK, but I've noticed the water pressure is low.
If I turn on the cold tap when the hot tap is running, the hot tap slows to a dribble.
Also, if I'm taking a shower and someone in the house turns on a hot tap I get scalded/frozen!!!

I've never lived in a house with a combi boiler before - Is this normal???

If this is normal, is there any way I can increase the water pressure (safely!)?

PS: I've cheched the pressure on the boiler and it is within the pressure range the instructions on the boiler states is normal.

uncle_buck_3

The Pressure gauge on a combi boiler is nothing to do with the water pressure that you have coming from the taps in your house.

The pressure gauge on the boiler shows the pressure that the Central Heating (CH) system has in it, normally around 1 bar when the system is off & cold. If you remove any water from the CH like when bleeding radiators this reading will fall & you will have to add more water to the CH system with the filling loop that is near or incorporated into the boiler.

As for water flow….
With a combi the cold mains water goes in & it’s heated instantly to provide hot water out… so the faster it goes through the boiler the less heat it will pick up, most combi boilers have a flow restrictor in them to slow the flow of water through them so it has time to heat up.
So when you are running your hot tap you are in effect just drawing water from the cold main…so if you open a cold tap the flow from the hot is bound to drop noticeably….I hope I’ve explained that ok.

If you are used to a conventional hot water system (hot water tank) a combi does take a bit of getting used to…a general rule for most combi boilers is one draw off point at a time (one tap open at a time)

Also when the weather is cold you will notice that it takes a bit longer for the hot water to reach the tap…this is because the cold water coming to your house / boiler will be colder at this time of the year than in the summer.

Have a look at this link for more info on combi boilers.

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


Ub.

beachbum_3

Uncle Buck summed it up really but.......... We've recently had a combi condensing boiler fitted and it is a pain sometimes. Running the childrens baths can seem to take ages but you soon get used to it. As for the shower, we've got an electric shower with water taken direct from the mains. With our old boiler only the cold tap affected it (I'M GONNA THROTTLE WHOEVER JUST FLUSHED THAT TOILET ETC!!), Now though its the hot water tap as well. Nothing you can do, just get used to it.

BB

moneysavingplumber

tollanarama wrote:

Also, if I'm taking a shower and someone in the house turns on a hot tap I get scalded/frozen!!!

I've never lived in a house with a combi boiler before - Is this normal???

Consider changing your current shower arrangement for a thermostatic shower mixer that will minimise the effect of sudden pressure changes due to taps being opened elsewhere and will re-balance the temperature automatically.

tollanarama wrote:

If this is normal, is there any way I can increase the water pressure (safely!)?

If your cold mains inlet pressure is low it could be for many reasons, but it will have to be checked before you will know if it is adversely affecting the performance of your combi, most have specified minimum and maximum operating pressures, and pressure is not the same as flow rate. Most combis deliver a flow rate of between 9 and 12 litres a minute at a 35 degree temperature rise, which can be checked with a flow cup, available from plumbers merchants and probably screwfix or similar.

tollanarama

Thanks all for your replies!

Basically, I've just got to get used to it. - No problem, I just wanted to check that this was normal.