Bosch Highflow 400 - non condensing type

[mayurw]

I have had this boiler now for around 12 years and it been fine but recently it has started to play up. While the central heating is on and a demand for hot water is called for, once the tap has been closed the red light above the CH temperature dial starts flashing and the heating fails to resume. The only way to get the heating back on is to reset the boiler back turning the temp dial all the way back down to zero and back up. This doesn’t happen all the time and is intermittent but any help/advice is appreciated

Thanks

 

[JohnHarrison]

It sounds like the plate heat exchanger is blocked. It happened on mine. Descaling and cleaning sorted it.

 

[mayurw]

so it sounds like I need a powerflush? is there anything else I should be looking out for?

Thanks

 

[mayurw]

So I have now powerflushed the system but I still have the problem but it doesn't happen so frequently. Reading on the forum I see that its the DHW heat exchanger that needs to be cleaned and remove and to this is not a simple job. So I have brought some DS-40 which I will add and leave in the system for no more than 4 hours as I'm told I have a aluminium heat exchanger? also which wires do I need to remove so I can run the hot water without the burner being on? I read somewhere on this forum I could do that.

Thanks

 

[JohnHarrison]

So I have now powerflushed the system but I still have the problem but it doesn't happen so frequently. Reading on the forum I see that its the DHW heat exchanger that needs to be cleaned and remove and to this is not a simple job. So I have brought some DS-40 which I will add and leave in the system for no more than 4 hours as I'm told I have a aluminium heat exchanger? also which wires do I need to remove so I can run the hot water without the burner being on? I read somewhere on this forum I could do that.

Thanks

If the primary side of the plate heat exchange is blocked fit a magnetic filter on the return pipe to stop it happening again. If the secondary (fresh water) side is blocked then take water hardness prevention measures.