Linea 28 lockout?

[niggle]

Our Linea 28 has performed faultlessly for the first 3 years but recently it started playing up.

The design is such that if the boiler fails to ignite within 8 - 12 seconds of DHW or CH demand then the boiler will shutdown and go into "lockout". The status LED will turn red and the code "01" will flash on the temperature display. The boiler can be reset by switching it off at the mode selector switch and then back on again.

Occasionally our boiler will behave as if it is in lockout mode, except that the status LED remains green and no error code is flashing on the display. Resetting the boiler via the mode selector switch/dial fixes the problem and the boiler will then fire up instantly.

I have followed the flow charts in the Vokera manual and testing with a DMM shows that the DHW flow switch is closing but the pump is not being energised. The manual suggests that this is a PCB fault and this makes sense, the pump relay being the obvious suspect.

I replaced the PCB a few weeks ago and all was fine until last week. The problem now appears to have returned and testing again shows that when a hot water tap is opened the DHW flow switch is closing but the pump is not being energised. The boiler runs fine after resetting.

I am reluctant to believe I am unlucky enough to receive two PCBs with the same fault. I guess the processor on the PCB could lock up if the power supply to the PCB was dirty but that would be very difficult to prove.

Does anyone have any other suggestions?

 

[Agile]

Now was the replacement PCB really a NEW manufacturer's PCB ???

You clearly have the understanding to repeat your previous tests to see if the problem is on the pump relay.

Why not renovate the old PCB by replacing the faulty pump relay?

Tony

 

[niggle]

Now was the replacement PCB really a NEW manufacturer's PCB ???

You clearly have the understanding to repeat your previous tests to see if the problem is on the pump relay.

Why not renovate the old PCB by replacing the faulty pump relay?

Tony

Thanks for replying.

The parts supplier assured me that the replacement PCB was a genuine new PCB sourced from Vokera. However, taking into consideration the fact that the first replacement PCB from this supplier arrived with a rusty transformer, a blown fuse and an obvious board fault that blew any replacement fuses, I'm not so sure...

I have not proven that the pump-relay is to blame when the fault occurs. There's mains voltage all over the board and I've had several belts already. If I disconnect the mains to work on the boiler safely that resets the PCB and the problem "goes away".

There's a lot going on on the PCB between the DHW switch input and the pump relay low-side. I would need to solder some test-points onto the pump relay low -side and leave the board installed until the fault occurs again. A proper schematic for the PCB and the source code for the microcontroller firmware would be nice too. At least then I could be sure that the microcontroller is still running when I get the apparent lockout.

 

[Rob]

nevermind!

 

[Agile]

Unfortunately you cannot get any CCT diagrams for boiler PCBs.

Some of the firms that repair pcbs have done some tracing of the simpler boards with discrete components.

As the Linea is a relatively advanced design with surface mount components that would be a two week task and you would still not know what the custom components were or the routines in the controller.

Rather than solder test leads on the pump relay you could use a magnetic detector stick or use a linear Hall effect detector to see if the coil is powered.

I think that your boiler has a system flow switch on the left hydraulic block which has to be activated after the pump is powered and before the gas and ignition circuit is powered. If so I assume you are aware of this.

You have to understand that the manufacturers write the books for ignorant plumbers and not for electronics experts!

Tony

 

[niggle]

I think that your boiler has a system flow switch on the left hydraulic block which has to be activated after the pump is powered and before the gas and ignition circuit is powered. If so I assume you are aware of this.

You're right, it's located just to the right of the diverter valve (and I wasn't aware of this until now). It does come into effect - but only after the pump has started (to check primary circuit pressure before the gas is ignited). The problem I have is that the pump won't start in the first place.