We recently had a combi boiler installed in our rented property. Initially the plumbers left the cold water feed from the tank in the loft so the combi boiler was only supplying the hot water. Unfortunately due to the differing pressures (i think), the cold water feed was excessive whilst using the shower the overflow pipe from the loft rained from the side of the house.
The plumbers have since rectified that problem by removing the cold water tank and using the boiler to supply both the hot and cold.
Unforunately the water pressure is now so low that it takes 30 mins to fill the bath. Also the shower now operates too hot and eventually (after a few mins) runs cold then hot again.
Any help would be appreciated.
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A combi boiler is only supposed to be supplying hot water and heating your radiators, removing the tank in the loft means your cold water supply is coming directly from the mains, so your lack of pressure could be either the stopcock isn’t fully opened, the water company has a fault on the supply line causing a reduced flow or the plumber has erred somwhere.
This is a common problem with combi boilers, You may have good pressure but have a bad flow rate, because the boiler has an in built pump you cant use a pump for the bath / shower. The tank in the loft and the cylinder gave you the ability to have a reserve with good flow rate via the pump.
You now have to get the plumber back in to resolve the issue, they shouldn’t have recommended a combi if the pressure and flow rate weren’t correct, if you have no luck with the plumber go to your governing body ie Corgi in the uk to get advise, they will back you if it is proved the plumber is at fault.
A friend of mine is in exactly the same position having now spent £3k corgi are helping to sort this out.
Hope this helps.
You can set the water flow rate through the boiler, although your installer should of checked it before commissioning the boiler. If you look in the installation instruction’s it should tell you how to change it. If you do not have enough water passing the heat exchanger the boiler will go to low fire or drop the flame out until it cools which explains why your water runs hot and cold. You will never get the same flow rate as you had (when you had a storage tank), as even the best combi’s normally only give you 12 litres per minute, but it should be better than you are currently getting. If you get stuck call the fitters back.