pulsacoil A - trouble shooting. what to do next?

I have got a pulsacoil A class heater, which only heats up with boost. Am a electronic engineer and some background in electrical engineering too, so thought I will try and trouble shoot myself. Started with common online reported issues.

1) Checked the resistance on heating elements
peak(top): 18.7ohms
offpeak(bottom) : 18.2ohms

2) Nothing looks burnt. Pulled relay out and looked okay.
3) check out the fuse on main board. checked for continuity, OK
4) checked the 2 fuses on the left of relay, checked for continuity, OK
5) no leaks in the tank

- Turned on the switches for both peak& off peak, the 8 segment display showed "u 1" ? not sure what that means
- coincidentally, after few minutes the offpeak(afternoon session)circuit came ON and I could hear the relay clicking. The led, which was blinking before(i.e boost available) turned off(i.e normal)

Now, I don't know what to do next ?
How do i check the sensors? (using my multimeter)
Does the reading for heating element look okay to you?

Would be of great help if any experts here can provide any pointers.

Thanks in advance.

You checked the heaters
Around 19 ohm's is ok.
You checked the heaters to Earth.

Ref the display / segment you mention. That is in the book / manual.

Did the relay click or kept clicking?

I always connect a supply to the off peak so I have both ON & OFF peak supplies at the unit.

Now remove the off peak supply.
Put boost on ensure ON peak relay etc all work and supply to ON peak heater.

Now make OFF peak supply live.
The boost / ON peak heater should switch off straight away and off peak should work.

If you think you have a relay problem then swop the relay around. The off peak has done more work.

There are relays on the main ACB also.

If you read the book, it will take you through the ACB / fault codes.
Spend more time on the book and you will get there.

The early model had a GT490 ACB

Later ones have a different one.

Mike