hello there,please could you help! when we turn on the hot water it runs red hot for about ten seconds,then it runs cold for thirty seconds then hot then cold and so on the make of the boiler is a sabre it was only installed 4 weeks ago! i have tried turning the boiler on to water only,this makes no difference,i have turned every radiator off and put the boiler on to water and heating this also makes no differnece i have turned the water inlet down slightly this makes no difference the pressure guage is at 2.8 bar also the radiator pipes under the floor make a load of noise if you turn the radiators of individually,please help!,,,,,kirky