Firebird fault finding

[Murphyy]

Hi,

Can anyone help with the below?

I have a firebird C20 oil combi. Yesterday the hot water stopped working and the lock out light was on.

Reset the boiler and it was calling for hot water without a tap open, couldn't get the heating to work as from what I can make out the hot water over rides the heating. Did a google search and could be the flow switch but this model has a red flow thermistor.

To get the heating working I disconnected the flow thermistor but it through a fault and the green LED flashed between the hot water and heating so I then disconnected the electrical supply to the hot water on the PCB and the heating is now working but as soon as I reconnect power to the hot water terminals it calls for hot water again without a tap open.

The resistance on the flow thermistor terminals are around 50ohms raising to over 100ohms when a hot tap is opened.

Anyone familiar with this boiler? Is the red flow thermistor knackered or are those readings normal? It seems to be detecting a flow or could a relay on the PCB be knackered although I cant remove them.

Cheers for any advice I'm now stuck and typical it's the weekend with no merchants open.

 

[oilhead]

You have answered your own query. The boiler gives priority to Hot Water. If you think about it, it makes sense. It will probably only run for 5 mins or so to heat up the heatstore.
Lockout is a burner condition that is unaffected by the external controls. You need to check the burner function to find the cause of lockouts. The control box has a diagnostic sequence to help you. Take a look at the fault finding section in your handbook.

 

[Murphyy]

Cheers, just gone through that after I posted and found the sensor temp/resistance chart. Looks like I'm getting no voltage at the flow terminals on the PCB.

The boiler has now stopped continually running and calling for water but the hot water LED remains on.

 

[oilhead]

Have you checked for overheat stat tripping? Bypassing the HW connections on the PCB may well have meant you have had the burner running with the wrong pump for the controls and overheated the boiler.

 

[Murphyy]

The lockout light only came on once when I noticed the water had stopped heating and no other warning lights and nothings ever tripped. I've had my volt stick on the pumps and it appears their both running when they should.

I'll see if I can get a replacement flow thermistor tomorrow as only £15 and if that doesnt work I'm going to have to get someone in to have a look.

I'm about as far as my knowledge will take me cant think what else would make it think water is flowing through the hot taps when it's not.

 

[oilhead]

If the boiler is not running, then the heatstore will be cold. The boiler gives priority to hot water, so although you don't have a tap running, it will still run to heat up the heatstore. Once the heatstore is up to the preset temperature, you will get heating.