Immersion Heaters

[maguire]

Hi All Should immersion heaters be on a FCU and is butyl required
Ta

 

[wingcoax]

Ideally they should be on their own circuit. But yes they can.

 

[ericmark]

There is no requirement for immersion heaters to use FCU and it was very common at one time to use 15A round pin plugs so Plumbers could remove and replace without an Electrician on site.

However although the 13A Plug is rated 13A it is not really man enough to run an immersion heater.

Use of butyl or any other high temperature cable is down to manufacture to stipulate but I would always use cable rated at 90 deg C to be on safe side.

The 17th (BS7671:2008) does however suggest that any appliance over 2Kw should not be powered from ring main. As shown in this PDF Corrigendum at end of corrections. And where 15A or 16A plugs are used these are not fused so supply would need to be dedicated anyway so consumer unit 15A fuse or 16A MCB will protect.

Because some are fitted to tank side and others go in from top there must be different temperatures within the units.

The other point is selection of thermostat. With metal or reinforced plastic there is no problem but with some cheap plastic tanks if the thermostat fails on it can boil water in header tank (It will boil in all types of tank) and with some this can cause the tank to fail cascading boiling water to those below. So to counter this thermostats with non resettable safety cut outs should be used.

 

[BS3036]

thermostats with non resettable safety cut outs should be used.

Do you really mean non-resettable, Eric? Or just resettable? I'd be annoyed if a single over-temperature event meant I had to buy another thermostat.

 

[Stoday]

The other point is selection of thermostat. With metal or reinforced plastic there is no problem but with some cheap plastic tanks if the thermostat fails on it can boil water in header tank (It will boil in all types of tank) and with some this can cause the tank to fail cascading boiling water to those below.

The "header tank" cannot get hot if it is plumbed in correctly. It will only get hot if hot water from the DHW cylinder circulates through the feed cistern. That is, the hot water rises up the vent pipe, flows into the feed cistern and down the expansion/feed pipe back to the HW cylinder. That will only happen if the vent pipe terminates too close to the cistern overflow level and/or the feed pipe is not connected to the cylinder below the immersion heater.

 

[ericmark]

thermostats with non resettable safety cut outs should be used.

Do you really mean non-resettable, Eric? Or just resettable? I'd be annoyed if a single over-temperature event meant I had to buy another thermostat.

Yes non resettable idea is if it fails once it is likely to fail again so for safety whole thermostat should be changed.

With metal tanks or the special reinforced types as used with solid fuel heating then you have re-settable type as solid fuel stoves can and do boil the water from time to time and as you say all you want to do then is push reset button.

I suppose there is a case for resettable with any duel powered heating system but if your central heating can boil the water in a cistern then something serous is going on. BS7671:2008 says that any electrical controlled item which you can touch made of metal should not exceed 80 degs C so it has gone well over limit before failing. And only a pressurised sealed system could exceed 100 degs C.

The "header tank" cannot get hot if it is plumbed in correctly. It will only get hot if hot water from the DHW cylinder circulates through the feed cistern. That is, the hot water rises up the vent pipe, flows into the feed cistern and down the expansion/feed pipe back to the HW cylinder. That will only happen if the vent pipe terminates too close to the cistern overflow level and/or the feed pipe is not connected to the cylinder below the immersion heater.

Read this proof of pudding is in eating.

 

[londonboy]

I think eric means cold water storage cistern as opposed to header (f and e) tank.

Faulty immersion stat > boiling cylinder > heat rising into storage tank.