Worcester Bosch 350 combi - Hot water is too hot.

Question

My combi boiler generates hot water too hot; I can't get the installation instructions from Worcester. Any ideas where I should start looking?

Answer 1

If the boiler has a domestic hot water control k**b on the front then turn this down.. If it hasn't, or you've already tried this, then it's possibly the hot water thermistor that is at fault. These are relatively cheap and easy to fit. If this is faulty then it is not sensing the hot water temperature correctly and therefore is not telling the boiler to stop heating when the water is at the required temperature.  

Answer 2

The temperature thermistor could be faulty,a faulty modulating coil on the gas valve could also cause the water to over heat.The flow rate on the boiler might not be adequate and may need increased,11 litres per minute will be adequate,you can check this with a stopwatch and a measuring jug.If you have a hand held thermometer,fill a cup with cold water then measure the temperature.Run the hot water then measure the temperature,you should have a difference of 35 degrees c,if its in excess then you have a fault,if its within these parameters then it could be down to the warm weather and the cold water coming into the boiler being less cold.

Answer 3

Turn down the dhw control k**b on the boiler. If this doesn't improve the hot water you must have a dhw thermistor gone faulty.  

Answer 4

I have the same boiler, and had the same problem. My Corgi Service engineer removed the tiny white plastic flow restrictor in the boiler and now the problem has gone away. Recommendation - You can ask your boiler service agent to do this for you - do not try and DIY. Another thing you can do is to check that the stop valve of your incoming cold water main is fully turned on - water starvation will cause the boiler to overheat the water too.