BG 330 gas boiler - intermittent fault

[DMANDMSMITH]

F5 fault

Happened first time ~18 months ago

• Plumber called in – overheat thermostat had triggered – push reset – OK ~12 months
• Started doing it increasingly frequent intervals – now almost every few days
• Replaced overheat stat, checked connections, still doing it

Fault finding flow chart page 34 manual – no air in system & pump wired into boiler & not into programmer.

Watched boiler & pump yesterday & it malfunctioned

• Operating OK 67C/53C & pump running (max flow)
• Click from boiler – relay? – pump switched off but boiler still operating
• Temperature rose to 85C
• Few minutes later, click & pump came back on, boiler temp dropped back to normal & boiler fired up. Temperature range 67/53C
• Repeated this click – pump off/pump on at random intervals
• Switched off boiler to reset, no difference
• Overheat stat didn’t trip

Pump (Grundfoss Alpha 2) seems OK when it’s getting power from boiler

No signs air in system

Overheat stat seems OK – in any case didn’t trip as I'd turn down the boiler temp for fault finding

Fault seems to be that Boiler control unit is randomly switching off pump

Don’t want to be ripped off by plumber – any opinions?

Known fault?

Replace boiler control board?

Any help much appreciated!

 

[Agile]

The fault seems to be that the boiler sometimes turns off the pump.

Then the boiler overheats and the overheat stat turns the boiler off to protect it.

So everything between the supply and the pump needs to be checked.