Unvented cylinder swap immersion heater weird

Joined
2 Nov 2010
Messages
3,424
Reaction score
516
Location
Humberside
Country
United Kingdom
This is just plain weird.

Swapped a system from vented hot water tank to direct twin immersion heater unvented tank.

Electric only house so added timer and a top/bottom switch so they can swap between upper immersion and lower immersion. This is powered from the old immersion heater switch.

Now comes the weird bit. Switched on and nothing. Checked with a multimeter 240v at the immersion.

The house does have electric underfloor that uses off peak but I don't think this is involved.

Checked all the way through thermostat is on immersion checks out resistance. Wire the immersion up directly to a normal plug socket. Immersion comes on and draws current I can see this on the meter.

Wire back up to the old immersion heater switch but use a 1.5kw blow heater as a load. Blow heater comes on no problem?? Back to the immersion and nothing.

Luckily the plug is convenient so wire the whole thing up to that and it works fine. Something is weird about the old immersion heater switch.

All I can think is a problem in the earthing at the old immersion heater switch? Immersion heater switch itself with a high resistance? Old immersion heater cable?
 
Sponsored Links
Joined
30 Jun 2009
Messages
21,627
Reaction score
2,568
Location
Londonderry
Country
United Kingdom
At what points of reference are you getting 240V?
Live to earth and live to neutral. You may have a faulty neutral across the switch.
 
Joined
3 Nov 2006
Messages
27,288
Reaction score
3,007
Location
Bedfordshire
Country
United Kingdom
Are you qualified to work on un-vented hot water cylinders and understand the need to have pressure and over heat safety sensors fitted to the tank that will cut off power to the immersions.

Without these the tank may explode in a fault. Not only from an immersion remaining powered and the water boiling but also from an explosive mixture of hydrogen and oxygen from electrolysis of water from a corroded element.
 
Sponsored Links
Joined
2 Nov 2010
Messages
3,424
Reaction score
516
Location
Humberside
Country
United Kingdom
Are you qualified to work on un-vented hot water cylinders and understand the need to have pressure and over heat safety sensors fitted to the tank that will cut off power to the immersions.

Without these the tank may explode in a fault. Not only from an immersion remaining powered and the water boiling but also from an explosive mixture of hydrogen and oxygen from electrolysis of water from a corroded element.

Yes thank you.
 
Joined
30 Jun 2009
Messages
21,627
Reaction score
2,568
Location
Londonderry
Country
United Kingdom
So you measured, 240V at the load side of the immersion heater isolation switch across L-N with switched closed?
If that the case can only assume that you had not terminated the load side to the switch contacts correctly, could have been insulation trapped or loose in terminal.
 
Joined
14 Sep 2006
Messages
6,343
Reaction score
385
Location
Gloucestershire
Country
United Kingdom
If you have 240/230V at the element terminals and the resistance reads approximately 19Ω then the heater should work. Have you carefully tried a clamp on ammeter ?
 
Joined
19 Jan 2007
Messages
4,289
Reaction score
394
Location
London
Country
United Kingdom
So you measured, 240V at the load side of the immersion heater isolation switch across L-N with switched closed?
If that the case can only assume that you had not terminated the load side to the switch contacts correctly, could have been insulation trapped or loose in terminal.

I'd go with the above.

Have you checked the switch and made absolutely sure the LNE supply and load sides are correct, have you used continuity on a MM and checked the switch isn't duff?
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Top