Faulty flowswitch

[Graham3232]

I have a 7 year old Worcester Bosch Greenstar Heatslave 18/25 oil combi boiler. I have a reoccurring problem every few days with the flow switch sticking in the open position and causing the boiler run in HW mode and eventually cut out on the overheat thermostat. The water at the taps is then scalding hot from the internal storage tank.

I know this has been posted before a few years ago by others, but I have had 4 new flow switches and still no solution. I’m hoping someone else has…? Any help much appreciated!

I have a magnetic scale filter on the cold water inlet although it is a soft water area. I have eliminated any leaks on the HW pipework and also tried fitting a check valve on the HW outlet on the advice of the service engineer.

 

[AngelesPlumbing]

Im not being horrible, will u call gas safe engineer?

 

[picasso]

Im not being horrible, will u call gas safe engineer?

Bit pointless kevin as its an oil boiler

 

[AngelesPlumbing]

Oftec

 

[Graham3232]

I’ve had an OFTEC engineer service the boiler every year and replace the flowswitch three times! I have replaced it again myself. You don’t need a Gas Safe or OFTEC engineer to replace a flowswitch, it’s only basic plumbing. I only had it done by OFTEC as the boiler was under a 5 year warranty. Now it’s out of warranty I’m sick of this ‘design’ fault and am looking for someone who has found a solution… Any help is much appreciated.

 

[jeff the gasman]

Boiler should switch off on stat anyway. I think you have a faulty pump or similar. Have you checked the flow switch and hot water stat or have you just assumed it's the flow switch.?
Jeff

 

[Agile]

Do you know EXACTLY how the boiler flow switch had failed?

It makes no sense just to replace a part many times without diagnosing why its repeatedly failing!

In addition sounds like there is a temperature control fault as well.

Tony

 

[oilhead]

The flow switch on this boiler is a magnetic proximity switch. How far away is your scale conditioner?

 

[Graham3232]

Thanks for the replies. The HW thermostat has also been replaced twice! The magnetic scale inhibitor is about 1m away from the flow switch on the CW supply pipe and has been added last year to try and stop the problem. I have checked with a multimeter to confirm the flow switch ‘on’ and voltage back to the boiler when there is no HW demand. The flow switch overrides the HW thermostat.

 

[oilhead]

The flow switch will override the DHW thermostat. Do you still have the gauze filter fitted on the cold inlet?
I have found that the flange seal on these degrades and leaks. Is it possible that some of this seal has jammed the switch?
When changing now, I usually substitute a rubber seal for the manufacturer's own.

 

[Graham3232]

It does have the gauze filter and yes this has leaked in the past but it is replaced each time the flowswitch is replaced. I am thinking of moving the flowswitch and putting it vertically on the supply pipe in the hope that gravity will keep it closed when there is no flow?! I also noticed the newer versions of this boiler have a turbine switch and hall effect sensor but that would require a PCB for control. Has anyone fitted a shock arrestor on the CW supply or a pressure reducing valve to any effect?