Older Immersion Heater Replacements

blw25

Hi all,

I've just moved into my first home and need to fix up our hot water supply. Some photos below... We currently have:

- Electricity only
- E7 tariff
- Old gravity-fed immersion system with newer digital timers (not sure they're set up to match E7 setup)
- Scorch marks on thermal foam by boost/sink element connection
- Seriously low pressure and flow in all hot water taps AND toilet refilling

Does anyone know of a good green system to go for that doesn't require outside work such as warning pipes etc? We don't want the rigmarole of freeholder permission and associated feed £250+

Currently looking at Mixergy as well as other systems similar to that already installed. Don't want to waste money without significantly improving energy usage.

Have seen several options but very unsure what is best. Might even just need a service and descaling of the old system?

Any help much appreciated

Bill

QrizB

Those scorch marks on the foam aren't directly from the immersion. They make me think the last plumber to change the immersion element had to take a blowlamp to it to loosen the connections.

Low pressure goes hand-in-hand with gravity-fed systems.

You say "your new home" and mention the freeholder. I take it you've bought a lease, and aren't renting? Depending on the lease you *might* be free to change pretty much anything that isn't structural.

coffeehound

So the cold cistern is directly above the hot water tank — yes that will be very low pressure. Best to get a plumber to advise what options you have based on the mains pressure and flow measured in-situ

Re the immersion heaters, really you should only need to use the bottom one — heated only during your E7 hours of course. The top one should be switched off unless needed for a boost during the day.  

Best to verify your E7 times by watching when the meter switches between registers.  You could post a photo of the meter to get more details if required. 

blw25

Heya,

Thank you for the reply - that’s great about the scorch marks - did think it very odd! 

First purchase and it’s leasehold flat yes. One company I briefly spoke to said an unvented system, utilising the excellent cold water pressure from mains, needs external work. No other flats have these warning pipes so I’m unsure we’d get permission and it costs to even ask.

 Will double check the lease but anything going through External walls might be considered structural I guess…

blw25

coffeehound said:

So the cold cistern is directly above the hot water tank — yes that will be very low pressure. Best to get a plumber to advise what options you have based on the mains pressure and flow measured in-situ

Re the immersion heaters, really you should only need to use the bottom one — heated only during your E7 hours of course. The top one should be switched off unless needed for a boost during the day.  

Best to verify your E7 times by watching when the meter switches between registers.  You could post a photo of the meter to get more details if required. 

Great thank you! I’ll set it up to test it tonight. The pressure is more of an issue than figuring out the timer but there’s not much to do with the storage tank right above the heated tank.

EssexHebridean

First up - congratulations on your new home!

We've got an inline pump fitted to boost both the hot water from the immersion and the cold flow from the header tank to bathroom taps and cistern. It's mostly pretty quiet - although gets a bit noisy when running for a while running a bath for example. the first one we had fitted by a plumber, that lasted around 5 years and we fitted its replacement ourselves, last year. It means we have almost the same flow to the taps in the bathroom as we have with a straight mains cold supply on the kitchen cold tap. It's a low tech solution, but it works! 

Not sure where you are but currently in East Anglia and supplied by Utility warehouse our electric switches to E7 at just after midnight, and back again at just after 7...you may hear an audible click as it switches over. 

blw25

Brilliant thank you! A pump might be the solution is it isn’t a hard water issue blocking pipes… we’re in SE London but I’m going to investigate tonight at midnight 🕵️‍♀️ 

doodling

Hi,

There are several options:

1. Keep what you have now and improve the plumbing / add a pump to improve flow / pressure.  This is probably the least disruptive approach.
2. Go for an unvented system.  This will allow the cold water header tank to be eliminated but will require a pipe to the outside for any discharge from from the over temperature / pressure valves (which will leave the tank around waist height).  Your existing header tank (which would disappear in this scenario) has an overflow so you might be able to use that pipe route for the discharge but it would need to be plumbed in copper, not plastic.
3. Go for a heat store system.  This will provide mains pressure hot and cold without requiring the external pipe but is a less common solution than the other two and therefore may be more expensive / harder to find competent tradespeople.
4. Ditch a stored hot water system and heat on demand i.e. an electric shower and local heaters for the taps.  Most people find the performance of such arrangements disappointing however and you can't use such a system to fill a bath - there is a risk of devaluing the flat if you do this.

Observations:

• I wouldn't worry about the scorching of the existing tank, whatever the source of the scorching was isn't there now.
• If you retain the existing tank then it could do with a lot more lagging.
• How guaranteed is your water pressure?  Relying on mains pressure is generally OK, but if its a flat, are there times when mains pressure is poor?  Options (2) and (3) are reliant on good mains pressure.
• Whatever you do, you need to get to grips with the way in which you use the two immersion heaters.  Normally the bottom one should be controlled to match the E7 times.  The top one is generally intended to be used as a boost, if you run out of water during the day and you just need a little more - normally this would be controlled on a timer that runs for a fixed time - e.g. 1 hour.  Of course your specific circumstances might make this approach wrong for you - for example, if you don't use much stored hot water (e.g. because you have an electric shower) then you might be able to turn the bottom immersion off completely and control the top one to match the E7 times so that you are keeping a smaller volume of water hot.

blw25

doodling said:

Hi,

There are several options:

1. Keep what you have now and improve the plumbing / add a pump to improve flow / pressure.  This is probably the least disruptive approach.
2. Go for an unvented system.  This will allow the cold water header tank to be eliminated but will require a pipe to the outside for any discharge from from the over temperature / pressure valves (which will leave the tank around waist height).  Your existing header tank (which would disappear in this scenario) has an overflow so you might be able to use that pipe route for the discharge but it would need to be plumbed in copper, not plastic.
3. Go for a heat store system.  This will provide mains pressure hot and cold without requiring the external pipe but is a less common solution than the other two and therefore may be more expensive / harder to find competent tradespeople.
4. Ditch a stored hot water system and heat on demand i.e. an electric shower and local heaters for the taps.  Most people find the performance of such arrangements disappointing however and you can't use such a system to fill a bath - there is a risk of devaluing the flat if you do this.

Observations:

• I wouldn't worry about the scorching of the existing tank, whatever the source of the scorching was isn't there now.
• If you retain the existing tank then it could do with a lot more lagging.
• How guaranteed is your water pressure?  Relying on mains pressure is generally OK, but if its a flat, are there times when mains pressure is poor?  Options (2) and (3) are reliant on good mains pressure.
• Whatever you do, you need to get to grips with the way in which you use the two immersion heaters.  Normally the bottom one should be controlled to match the E7 times.  The top one is generally intended to be used as a boost, if you run out of water during the day and you just need a little more - normally this would be controlled on a timer that runs for a fixed time - e.g. 1 hour.  Of course you specific circumstances might make this approach wrong for you - for example, if you don't use much hot water (e.g. because you have an electric shower) then you might be able to turn the bottom immersion off completely and control the top one to match the E7 times so that you are keeping a smaller volume of water hot.

Thank you Doodling - brilliant layout of the options. Hasn’t thought about the current overflow being a shortcut. This would work provide the installation running to the drains wasn’t an issue. I’ll ask the company that suggested it.

100% correct with the timers - at the moment we’re not really using hot water because of the pressure issue (it’s pointlessly low) but we’ll get that sussed in case we need it anyway

 really appreciate the time you’ve taken - super helpful

EssexHebridean

Oh - on the boost switch if you DO need to use it - if you just need to add to the temperature of a tank that has had a few loads of washing up done from it perhaps, in order to have a bath in the evening, then literally about 20 minutes should do the trick. If you DO go down the root of the pump though, be aware that you can't run any amount of hot water while the boost is on without risking tripping the thermal cutout - it's more annoying than anything else although the location of the reset on ours does mean a mobile phone camera and a bit of prodding about is required in order to locate it. This occurs because the pump delivers more water than the tank would usually do on its own - so the fill from the header tank can't quite keep up! 

blw25

EssexHebridean said:

Oh - on the boost switch if you DO need to use it - if you just need to add to the temperature of a tank that has had a few loads of washing up done from it perhaps, in order to have a bath in the evening, then literally about 20 minutes should do the trick. If you DO go down the root of the pump though, be aware that you can't run any amount of hot water while the boost is on without risking tripping the thermal cutout - it's more annoying than anything else although the location of the reset on ours does mean a mobile phone camera and a bit of prodding about is required in order to locate it. This occurs because the pump delivers more water than the tank would usually do on its own - so the fill from the header tank can't quite keep up! 

Thank you - that makes sense but wouldn’t have worked it out myself! Still going to look at full replacement options to see if I can improve efficiency but the pump sounds like a very good option. TY  🙏