Question for Heating/Plumbing knowledgeable members

[macabethiel]

In the next week or so I am going to fit a new heating element in my water sylinder. The existing heater was new with the water cylinder 3 years ago so I do not expect any problems unscrewing the old element that is a short one mounted in the top of the water cylinder. I have the right tool to fit it.

When I replaced my last immersion heater some 25 year or so ago my tank was a Primatic one so I had to drain the whole heating system down. My new CH system is a fully pumped system with a motorised valve for the 3 heating options.

My question is this can I just switch off the hot water header tank, drain the hot water from the lowest tap in the house and remove the top mounted heater or do I have to use the bottom drain on the water cylinder and drain it completely as well?

[zippy656]

Pm terranosaurusdoug :-)

[solarman216]

You should have a gate valve on the feed to the cylinder, often in the same cupboard as the cylinder but could be on the outlet from the cold cistern in the loft, once this is turned off check its effectiveness by opening a hot tap, water will run till the pipes above are empty, then it should stop, if it drips at a fast rate you will need to drain some of the water from the drain at the bottom of the cold feed, but often the rubber on these sticks and goes hard so once disturbed be prepared to replace the rubber for which you will need to drain the whole cylinder, if the hot tap does not drip much then you can get away with wrapping a large towel around the top of the cylinder and remove the heater at which around a couple of cups of water will spill, this is assuming the hot draw off is close to the top of the cylinder, which it should be, you can then siphon off some water to enable you to dry off the area before fitting the new heater, only apply jointing paste to the washer and heater face NOT to the threads, or removal next time will be difficult to say the least, Rick

[macabethiel]

You should have a gate valve on the feed to the cylinder, often in the same cupboard as the cylinder but could be on the outlet from the cold cistern in the loft, once this is turned off check its effectiveness by opening a hot tap, water will run till the pipes above are empty, then it should stop, if it drips at a fast rate you will need to drain some of the water from the drain at the bottom of the cold feed, but often the rubber on these sticks and goes hard so once disturbed be prepared to replace the rubber for which you will need to drain the whole cylinder, if the hot tap does not drip much then you can get away with wrapping a large towel around the top of the cylinder and remove the heater at which around a couple of cups of water will spill, this is assuming the hot draw off is close to the top of the cylinder, which it should be, you can then siphon off some water to enable you to dry off the area before fitting the new heater, only apply jointing paste to the washer and heater face NOT to the threads, or removal next time will be difficult to say the least, Rick

Thanks Rick

[terranosaurusdoug]

Where abouts on the cylinder is the heater?, is it a standard cylinder with it inserted at the top? Also, if you decide to use the gate valve (red wheel) take it slow and gentle when opening it back up, often they break and remain closed so you have to replace the valve.
I prefer to turn off the water supply to the feed cistern for the cylinder, sometimes there is an isolation valve but usually just use main stop tap. Once in a while a float valve may stick due to dropping lower than usual but rarely, odds of that happening are low compared to odds of gate valve sticking, in which case water still needs to be turned off.

[macabethiel]

Where abouts on the cylinder is the heater?, is it a standard cylinder with it inserted at the top? Also, if you decide to use the gate valve (red wheel) take it slow and gentle when opening it back up, often they break and remain closed so you have to replace the valve.
I prefer to turn off the water supply to the feed cistern for the cylinder, sometimes there is an isolation valve but usually just use main stop tap. Once in a while a float valve may stick due to dropping lower than usual but rarely, odds of that happening are low compared to odds of gate valve sticking, in which case water still needs to be turned off.

The heater is top mounted. I have decided to switch off at the main tap and drain down. The float valve in the header tank is a brass one that I fitted about 5 years ago and is in good condition. I plan to do the job tomorrow.

[rayf3262]

The heater is top mounted. I have decided to switch off at the main tap and drain down. The float valve in the header tank is a brass one that I fitted about 5 years ago and is in good condition. I plan to do the job tomorrow.
Before you drain it down, I suggest you loosen the element first.
Or you may end up trying to stop the cylinder moving around when its empty.

[macabethiel]

Switched off the Central Heating and made sure Immersion Power was off with Spur fuse removed.Disconnected old Immersion Heater from wiring ensuring the neutral did not touch the earth after disconnect.

Removed wooden shelving from airing cupboard to make everything easier to see and enable removal of old heating element - turned out to be a 27" unit screwed in from top.

Then turned off cold mains in downstairs W/C. Left cold tap open in W/C sink in case of poor shut off. Drained hot water from bath tap.

I slightly loosened the heater about one flat after I had drained the Hot Water. Then I drained about 4 Gallons of water from the water cylinder bottom drain with pipe running downstairs and outside through letter box to outside drain.

I gingerly unscrewed the Immersion and then pulled it out - the water level was about 6" below the top of the tank. It was split open at the very bottom of the element on the U bend. No washer was fitted with PTFE tape.

Nipped into town for similar sized replacement 3 kW Immersion Heater with a Copper Element. PTFE tape to new Heater as no Boss on top of tank to seal against - a sort of raised threaded flange fitted to the water tank. Gently started thread by hand then tightened it up. Re-connected wiring,re-fitted shelving.

Water mains back on-went round taps to eject the air in the pipes both hot & cold. When header tank had stopped filling - switched on Central Heating and HW via CH. Checked for any sign of leak / water at Immersion flange. All dry, tested Immersion mains not tripped.

Total time including visit into Town to obtain part was 2 hours 15 mins. Total Cost was £18.60 including new roll of PTFE tape.

Thanks everyone who contributed to my appeal for help - I love this site!!