Sime super 90 intermitent DHW and CH

The boiler will fire and run for a short time but then cut out. The fan and pump continue to run then after a minute or so the gas will reignite. This makes running a bath of water impossible as the water runs intermittently hot and cold.

The fault is repeatable with just CH (Winter mode, Control full) The heating will reach temperature but it takes longer as for half the time the flue exhaust is cooling the exchanger instead of gas heating.

I have followed the manufactures fault diagram but due to the intermittent nature of the problem it does not help. Thermistors and limit stat have been checked for function and are good. Diverter and micro switches function Pressure is correct for maximum and minimum gas. Pressure can be reduced at potentiometer. My thoughts are control PCB, I would appreciate another opinion before I commission the work.

Thanks

I dont understand why you are "commissioning" part replacements!

The normal solution is to engage a heating professional to diagnose the fault and then do whatever is necessary to fix it.

However, when you have commissioned the replacement PCB and it still does not make it work you can get a competent CORGI registered person to check the fan/venturi/APS.

Tony Glazier

Agile said:

I dont understand why you are "commissioning" part replacements!

The normal solution is to engage a heating professional to diagnose the fault and then do whatever is necessary to fix it.

However, when you have commissioned the replacement PCB and it still does not make it work you can get a competent CORGI registered person to check the fan/venturi/APS.

Tony Glazier

Click to expand...

Thank you for your useful comments Tony.

I am well aware of the requirement to use a CORGI registered engineer. By Commisioning works I mean a CORGI engineer will fit. I live on an offshore island and well experienced engineers don't exist, they are more useful for arga and oil fired as gas is rare. If you fancy a holiday?. The reason I am making these enquirys is because the engineer is unsure, I was present during fault diagnosis and made the above observations.

I just need a second opinion before the cost spirals and was hoping someone could assist.

Which "off shore" island is it?

In that case get a competent CORGI registered person to check the fan/venturi/APS.

He needs to remove the venturi and probably wash it. The fan impeller may need washing too.

Merely blowing into an air tube is not adequate regardless of what he may think or say.

Gas is really much more pleasant and I would say easier to work with than oil. At least if any leaks it does not spoil yor clothes or the floor!

Tony