Back feed problems .

With reference to my  ...Right decision on EICR  Thread.....    we upgraded the board  to an  RCBO    14 way .   Three ways are separately  switched  for E7   Storage htrs   &  big Steinel   water heater  with E7   plus 24hr boost .

Bloody thing has a linked neutral in it which knocks the RCBOs out  .         We jump wired the  E7  contactor  coil  to get the off peak supply  on to the boiler .    

Two DP switches at the boiler   , 24hr Boost   &  Off Peak    .   I presume they feed the same element in the heater  , no info ,,also not our remit  to pee about with pressure vessel type thingys . 

The E7  out from the board  passes through the  contactor    N/O   which would  prevent the 24hr  Boost switch  from powering the storage htrs  at the same time as the W/Htr .    If 24hr  is switched ON  at night it   back feeds  through the  E7  DP switch  .         

That sounds like the old "sink / bath" immersion heaters.  two heating elements in one unit, one long and one short, used in a top entry tank so you can heat half the tank or all of it.  they shared a common neutral and you could get a "sink / bath" switch to go with them.

I have seen those used with the long element on E7 and the short element on a manual boost switch. Of course that linked the neutrals but in the days before any E7 circuits and the immersion circuit had an rcd it "worked"

I wonder if this is the same?

There is nothing to stop an electrician changing the immersion elements or rewiring an unvented cylinder.

New tenant moves in on Monday so I've replaced the  Water Heater  RCBOs  back to MCBs  .     But as I found out myself  ...if you replace the E7  DP switch because it was getting quite hot  ...you cop a pizzer  from the  flex  hanging from the heater    because the boost was ON .        

ProDave said:

That sounds like the old "sink / bath" immersion heaters.  two heating elements in one unit, one long and one short, used in a top entry tank so you can heat half the tank or all of it.  they shared a common neutral and you could get a "sink / bath" switch to go with them.

I have seen those used with the long element on E7 and the short element on a manual boost switch. Of course that linked the neutrals but in the days before any E7 circuits and the immersion circuit had an rcd it "worked"

I wonder if this is the same?

There is nothing to stop an electrician changing the immersion elements or rewiring an unvented cylinder.

Click to expand...

Im still learning....  not heard of one of those before

sprocketflup said:

Im still learning....  not heard of one of those before

Click to expand...

Yes  , dual element immersion heaters     , as Dave says  , "Sink & Bath type "  .     The short element in the top of the cylinder heated enough for a sink.    

The thing I was looking at is a Stiebel Eltron  pressure water heater ,  spoke to the guy who maintains them today , he confirmed there is only one element  in there  so the two supplies back -feed .