I hope you can help with a fault I have with my powermax 155x. Basically when running hot water from the taps, it will run hot for about 20-30secs and then run cold. The only way I have discovered to get hot water back on is to turn on the central heating so that the burner comes on. When the central heating turns on, the radiators get hot immediately even without the burner coming on, so there must be hot water in the system. Even with the hot water set to continuous and all day on the panel is still will not provide hot water unless the central heating is turned on and thermostat increased until the burner switches on.
Post by aaamusements on Aug 21, 2013 18:42:56 GMT -5
"2) Hot water runs hot initially then cools down. Most commonly caused by a failed thermostatic blender valve. A new valve fixes the problem. Less commonly the cause can be water scale. If the Powermax has an external plate heat exchanger this can be replaced quite easily and hot water is immediately restored. Many Powermax boilers have an internal domestic water heat exchanger and chemical descaling will be necessary. Not especially difficult but time-consuming and invasive. Involves bringing chemicals, a descaling pump, hoses etc into your house."
Post by Mike the Boilerman on Aug 29, 2013 13:39:26 GMT -5
There is another possible explanation. Given that the hot water works when the burner is running, this tells us the DHW flow switch is not responding to the tap being turned ON. Either the flow switch has failed or more likely, the heat exchanger is scaled and the water flow rate through it has become too low to operate the flow switch. (When the burner is running, the DHW pump runs but it it switched ON by a different circuit from the flow switch.) This effect can also be made worse by a failing blender valve.
Another reason for the flow switch not responding is it not being installed at the correct orientation. The flats where the cable enters it need to be vertical. Sometimes when someone repairs the common leak on a flow switch they don't realise this, and re-fit the flow switch with the flats at a random angle.
Appreciate this is a number of years later, but was wondering if you ever got resolution with this issue? I have an issue where the hot water to the taps slows to the point where it doesn't flow anymore, and am wondering if it is the blender valve causing the problem.
Thanks for the response ptelf - I think my problem is a little different to the one you experienced in that the flowrate of water to my taps drops to the point where it doesn't flow any more, which makes me believe it's a transient issue (i.e. a control valve) as opposed to a blockage (which would affect flow rate all the time). Did you ever notice issues with flowrate? Thanks, Max