About 6 months ago was asked to look at a fault heating (oil burner) not working and also no hot water. A quick flick with my over sensitive voltage stick showed supply was present at the controller the supply was was present but controller inoperative no indicator lights nothing. Not like the old days where a dry joint or burnt out resistor was detectable ,now sealed electronics so I had to get another one ,this fixed the problem. However this week got a call heating off again and no hot water. This time there was no supply at the controller or thermostat , the fault was the supply a 40 AMP 30mA DOUBLE POLE RCD 230V ZR40 BS EN 61008. Whoever installed a new boiler about three years ago correctly used a small 2way consumer unit RCD with a 6amp MCB along side it , one MCB spare. The RCD toggle had no switching action (not latch)even a bit of thumping no good. Now why would a RCD sitting in a consumer unit for three years never been touched switch mechanism go faulty. Even when taken out and replaced I could not get the removed one it to latch. Something is common to these two separate faults. Thinking along the lines could switching on a boiler oil burner unit at the same time as the circulating pump and other hot tank controls cause a damaging spike , its very odd. Don't know if the RCD has a electronic latch or mechanical latch , but I will go back and get it if not dumped and cut the dammed thing open to look.
RCDs do fail - a rather dated set of research ,and normally mechanical faults are corrosion or sticking of grease, unless it has been tripping and being reset a lot, when it might be wear.
Do not be too heart broken if cutting it open does not reveal very much.
There may also be a problem with surges/spikes but it is not easy to prove.
Any Voltage spike would be created when any inductive loads are disconnected surely? Or are you thinking of initial inrush currents? I am currently trying to educate myself on the inner deeper, darker parts, of oil fired boilers. The last one that I looked at had a 5 Amp fuse it its fused connection unit, rather that the 3 Amp size I usually find in gas boiler fused connection units. I believe that oil fired boilers may have an H.T. transformer to create a spark for fuel ignition. We don't normally have any problems with central heating circulating pumps do we, regarding spikes.
Is t possible that the faulty RCD was arcing just occasionally over a long time and the spikes created when this happened fried the electronics in the board??
Recently I was asked to check the electrical controls on a oil fired workshop space heater, as the owner thought it was an electrical problem.
I removed a few panels and searched the internet for its wiring diagram, then I spent three quarters of a hour with a tester and my Ipad checking wiring and electrical components.
Then I made the decision to stand up and kick the boiler with a size ten steel toe capped boot which resulted in it instantly bursting into life as a stuck float switch freed up.
The customer politely enquired why I had not just done that three quarters of a hour earlier. I replied that I needed to do enough investigation and testing to determine exactly how and where to kick it.
Amongst my testers I have a little used volt stick that will also determine if there is a magnetic field present, so you can get an indication that as well as a voltage being present at a solenoid there is also a magnetic field.
The controller and the RCD failing at separate times sounds unrelated to me, if they are related what’s the answer? Is it installing surge protection?
