Hello,
A few weeks ago I was asking here about powering my boiler from an inverter during a power cut. I have given it a go and here are my experiences and questions:
The boiler was fed by a fused connection unit. A poster, sorry I can't remember who, suggested that I replace the FCU with an unswitched socket and plug. He said that this fulfilled the requirements for isolation because the plug could be pulled out of the socket to isolate the boiler. Is the "unswitched" part important? I ask because I didn't have a spare unswitched socket so used a switched one, but I can easily go and buy an unswitched socket if regulations dictate. I'm trying to think of reasons why a switched socket might not be allowed. Does the switch only switch the live or is it a double pole switch? If single pole, I guess the switch cannot be used to isolate if it only switches one side but then a switched socket would still allow the plug to be removed for full isolation.
The boiler is oil-fired; does that makes a difference? An oil-fired boiler uses a pump to suck the oil. Does a gas boiler have a pump or does it just use the pressure in the supply pipe? The boiler manufacturer (Grant) said that the boiler could be used with *any* type of inverter. The boiler is connected to a Horstamn programmer and Horstman valves, as advertised in the Screwfix catalogue. I did contact Horstamn about using inverters with their products but never got a reply. The CH has a Wilo pump and sadly, Wilo did not reply to my questions either.
When connected to the modified sine wave inverter I had two problems:
- the controller has a back light dot-matrix LCD. When the inverter was used the back light and the LCD flickered. Also some vertical lines appeared on the LCD. Clearly the display did not like the waveform from the inverter but this seemed to be just cosmetic; the switching functions worked as intended.
- the boiler buzzed a lot. I think it was the boiler rather than the circulating pump but I will double check. I thought it was the oil pump or fan (or both). Whereas (1) was cosmetic and did not alarm me, I'm not so sure about this noise. Is it anything to worry about? Is it causing increased wear on whatever is making the noise? It will be only for occasional use but even so, should I upgrade to a pure sine wave inverter? The problem is these cost ten times as much!
I did also try to use lights powered by the inverter and both traditional filament and CFL bulbs seemed to work without any noticeable problems. One old CFL buzzed but new ones did not.
Thanks, Stephen.