Biasi Combi (model M96.24SM/c2)

[chriswills]

Hi,

When the C.h and the D.h.w are on together on my boiler its fine, but when i try to switch the boiler to D.h.w only, the boiler constantly keeps firing. I understand that when the switch is positioned in the D.h.w only position, the boiler should only fire to warm the water when a the tap is turned on. So in my case its constantly heating the water and im not even using it.
As a result of this i am having to exsinguish the boiler everyday before work to avoid wasteing gas and was wondering will this have any effect on the boiler?
Any advice would be most appreciated!!

 

[Slugbabydotcom]

IIRC these boilers don't react instantly when you alter the controls. It may run the fan and the pump after being turned off for anything up to a few mins to clear any excess heat.
If what you are telling us is right after allowing for this then its possible that there may be a flow switch stuck in the on position or a faulty /wrongly set frost stat or other control
Although there are plenty of safety devices in a combi, correct function should not rely on their constant use so I suggest you get an RGI out to check it over.
I've had a quick look at the MI's for this Riva compact HE and never saw an 'instant DHW' function so thats one possibility that can be ruled out.

 

[Agile]

You can see if the DHW flow switch is stuck on as sounds likely from what you say!

Take off the front cover if competent.

Look towards the right rear just to the left of the pump and see if there is a red LED illuminated.

If so then turn off the blue tap under the boiler by turning 90° clockwise. If the red led now goes out then you have a leak on a hot water supply pipe. This is not likely but needs to be checked before assuming there is anything wrong with the boiler.

If the flow switch is jammed on then there are two types, yours is expected to be the later type with a clear plastic Hall effect sensor/led housing. These are sometimes very difficult to remove as the nut has rounded off corners!

Tony