Intermittent hot water on WB Greenstar 30 Si

[halvid]

Hi,
I have a WB Greenstar 30 Si and I am having a problem where the DHW intermittently cuts out then comes back on after a couple of mins. It happens on all taps/showers including the kitchen tap. When the problem occurs the flame light on the boiler goes on and the fault indicator light stays off. Initially the problem mainly occurred on the upstairs shower only but over time seems to have spread to the downstairs shower and also downstairs kitchen tap.

This often happens even with just 1 person in the house having a shower and no other usage for hot or cold water, but it can be replicated by turning on the kitchen cold tap. Immediately the shower will go cold and the flame light off.

I understand that the cause could be the plate heat exchanger or DHW temperature sensor. Both have already been changed but to no avail.

Another suggested issue is low gas pressure at the meter, but I get an annual gas safety certificate and I believe this is checked during the inspection.

The only other remaining possibility that I have come across is a faulty or partially blocked flow turbine adaptor. Although nothing is leaking. Could this cause the problem I am describing?

I am a home owner looking to get some advice. Not going to do the work myself but just trying to figure out if it is worth trying to repair the boiler or perhaps go for a replacement. I know that Bosch offer a fixed price repair service but considering the plate heat exchanger and temperature sensor have already been changed, the options of the engineer seem to be limited. And there is no point paying £300 just to get the flow turbine adaptor replaced.

Many thanks,

Hans

 

[Deleted member 120897]

Try isolating the cold feed into the boiler and run the hot tap, if it still runs, then you could have a passing cold into the the hot, so like a failed shower check valve.

 

[halvid]

Try isolating the cold feed into the boiler and run the hot tap, if it still runs, then you could have a passing cold into the the hot, so like a failed shower check valve.

Thanks for the suggestion. However both showers are simple mixer taps and the hot water also cuts out on the kitchen tap.

 

[ShaunCorbs]

Do you know your mains flow rate ?

 

[halvid]

Do you know your mains flow rate ?

Don't remember off the top of my head but did check it several times using a flow measuring cup and it was well within the normal range and above the legal minimum.