Combi boiler DHW issue?

[SimonSime102]

Hi Everyone, I've had a look through the posts and can't seem to find the problem I'm having so thought I'd post a new thread just in case anyone can help?

I have a SIME Super 102 Deluxe combi boiler - around 9 years old. The CHeating is fine, it'll pump out hot water all day. My problem is with the DHW. It has never been great from the first day - always took some time to warm up but - not knocking it - it worked, it heated up and away it went.

It has now developed the following problem though... I turn on the HW tap and the boiler fires up. The water gets hot and away we go. Then the boiler cuts out - I think because the temperature is at it's hottest (If I turn the temp gauge up and down - it looks like it works fine - boiler stops after a relative amount of time) The problem is when it's cut out, it doesnt come back on unless I increase the water flow by opening the tap. But then the water's running too fast and doesnt get a chance to heat up? But this is the only way for the pressure switch to kick in and fire the boiler? So do I need a new Switch, Valve or Thermistor? Or something else????

Thanks in advance - Simon.

 

[bengasman]

what happens when you turn it up it bit further to begin with?
should not cut out that way.

 

[SimonSime102]

I turn the tap on, it needs to be about 1/4 open before the sensor (guessing its the flow sensor?) detects that I want hot water, then everything kicks in - boiler fires - water gets hot etc... The boiler reaches the required temp and cuts out. The water then goes cold? I have to turn the flow rate upto about 1/2 to 3/4 open to make it come back on. This is much too fast for the boiler to heat up the water to any reasonable temp???

 

[gas4you]

I don't know these boilers, but do they have a standard diaphragm? If so I would check this first.