Immersion Heater Help - PP120E

Wexi

Hi everyone,

I have a Santon Premier Plus PP120E (unvented direct immersion heater) fitted with two thermostats, which provides hot water to taps and shower. The central heating runs from a separate system.

On the PP120E:

- Bottom thermostat is set it to 4 out of 5 (approx. 60C), and connected to a wall mounted timer.

- Upper thermostat is set to 3 out of 5 and connected to a wall mounted Boost button.

Through some trial & error, I have found that the Upper thermostat is always activated and heating the water regardless of the Boost button being switched On or Off. I assume it cuts off at the set temperature (3 out of 5).

I am trying to cut down on energy costs and not have the immersion running outside of the timer function.

Questions

1. Is it safe to have the temperature gauges set to different temperatures on each thermostat?

2. If yes, and I set the Upper thermostat to 1, will it stop heating the water when I don't need it on?

3. Is there any way to use the Boost button / Upper thermostat as purely a boost function?

Hopefully that all makes sense. Any and all help is appreciated!

Thanks 

Reed_Richards

This doesn't answer your question but If your central heating runs off a gas or an oil boiler it would be much cheaper to use that boiler to heat your hot water, rather than relying on immersion heaters.  Are you sure that you don't already do that? Could that be why you think one of your immersion heaters is permanently on?

Wexi

Reed_Richards said:

This doesn't answer your question but If your central heating runs off a gas or an oil boiler it would be much cheaper to use that boiler to heat your hot water, rather than relying on immersion heaters.  Are you sure that you don't already do that? Could that be why you think one of your immersion heaters is permanently on?

Hi Reed,
The central heating runs off an electric system which is entirely separate - they have separate switches and controls so I'm confident one doesn't impact the other.
Cheers for chipping in! 

lohr500

Do you have an Economy 7 type electricity tariff? 

With an Economy 7 tariff, the bottom heater would normally be switched on during the off peak electricity period.
The fact that it has a timer would suggest this to be the case. But if so, you need to make sure the timer is correctly set to match the off peak electricity hours. (including any shifts between BST and GMT)

The top heater in an Eco 7 set up would be a boost only heater, used to provide a smaller volume of hot water if needed should all the hot water have been used up before the next off peak period.

It sounds from your description as though either the top heater has been incorrectly wired, or the boost button has failed. In either case a competent electrician should be able to diagnose the fault and fix it.

Once fixed, there is no harm in having the upper heater set at a lower thermostat level. In fact it would make sense if only small amounts of "boost" hot water were ever needed as less electricity will be used to reach the lower temperature.

There is a school of thought which says that if you don't need a full tank of hot water every day, then why bother heating a full tank in the 1st place. But with a well insulated tank like the PP120E I don't think there will be a lot of heat loss from the tank through the day.

If it was me I would : 

1. Get the boost button checked out, so it isn't heating the top half of the dank 24/7. Then only use it as intended to boost the water as/when needed.
2. Set the thermostat on the lower heater at the lowest level you can get away with to provide sufficient hot water for your needs. There is a small danger of Legionella bacteria if the water is stored below 60C. But in an unvented system, used regularly and filled from mains water my understanding is that the Legionella risk is minimal.

Others may think differently.

As a temporary fix until you can get the top heater/boost button sorted, is there a pop out fuse on the boost button, or a dedicated fuse in your fuse box that can you remove to stop the boost switch from supplying power to the heater?

As you suggest, turning the thermostat right down on the top heater might achieve the same result, but it could still heat to a lower temperature. However if the tank is fully heated by the lower heater set to a higher temperature, the water in the top half of the tank should in theory be hot enough to not trigger the upper thermostat to call for heat. However, if you use up all the hot water, then that upper heater could well kick in, even on the lowest stat setting so better to get the switch checked out. 

Wexi

lohr500 said:

Do you have an Economy 7 type electricity tariff? 

With an Economy 7 tariff, the bottom heater would normally be switched on during the off peak electricity period.
The fact that it has a timer would suggest this to be the case. But if so, you need to make sure the timer is correctly set to match the off peak electricity hours. (including any shifts between BST and GMT)

The top heater in an Eco 7 set up would be a boost only heater, used to provide a smaller volume of hot water if needed should all the hot water have been used up before the next off peak period.

It sounds from your description as though either the top heater has been incorrectly wired, or the boost button has failed. In either case a competent electrician should be able to diagnose the fault and fix it.

Once fixed, there is no harm in having the upper heater set at a lower thermostat level. In fact it would make sense if only small amounts of "boost" hot water were ever needed as less electricity will be used to reach the lower temperature.

There is a school of thought which says that if you don't need a full tank of hot water every day, then why bother heating a full tank in the 1st place. But with a well insulated tank like the PP120E I don't think there will be a lot of heat loss from the tank through the day.

If it was me I would : 

1. Get the boost button checked out, so it isn't heating the top half of the dank 24/7. Then only use it as intended to boost the water as/when needed.
2. Set the thermostat on the lower heater at the lowest level you can get away with to provide sufficient hot water for your needs. There is a small danger of Legionella bacteria if the water is stored below 60C. But in an unvented system, used regularly and filled from mains water my understanding is that the Legionella risk is minimal.

Others may think differently.

As a temporary fix until you can get the top heater/boost button sorted, is there a pop out fuse on the boost button, or a dedicated fuse in your fuse box that can you remove to stop the boost switch from supplying power to the heater?

As you suggest, turning the thermostat right down on the top heater might achieve the same result, but it could still heat to a lower temperature. However if the tank is fully heated by the lower heater set to a higher temperature, the water in the top half of the tank should in theory be hot enough to not trigger the upper thermostat to call for heat. However, if you use up all the hot water, then that upper heater could well kick in, even on the lowest stat setting so better to get the switch checked out. 

Thanks so much for the comprehensive reply!

Unfortunately I'm not on an Eco7 tariff. I live alone so I only require a small amount of hot water in the morning, then mostly taps in the evening. I've worked it out and overall I would end up paying more if I moved to Eco7, as the majority of my total electricity usage is throughout the day.

Yes I suspect the top heater may be incorrectly wired - the last plumber I used ended up having to wire it twice, and it was a quick in & out job... 

Completely agree - I don't need a full tank heated.  I'll have a plumber / electrician check out the Boost wiring - thanks.

In terms of temp fix, unfortunately both thermostats are connected via a single fuse on the switchboard. There's a pop-out safety switch but my understanding is that this is only activated by the thermostat itself. I don't think I can de-actvate it myself. I have also read in the Stanton manual the hat the upper thermostat should not be 'by-passed', although I'm not entirely sure if turning it off is considered bypassing it?
For reference, it's the Cotherm TSR 11″ T115 16A 250V.

Until I can get someone out, I will set the Upper (Boost) stat to a low setting, keep the Lower (timed) stat set at 4 out of 5 and hopefully this will reduce the energy used.

Thanks again, really appreciate your help!

Gerry1

You seem to be saying 'thermostat' when you mean 'immersion heater'.  The thermostat is contained within the immersion heater assembly.

The thermostat mustn't be bypassed (shorted out) because the water would boil, potentially explosively, if the safety cut out failed.

Wexi

Gerry1 said:

You seem to be saying 'thermostat' when you mean 'immersion heater'.  The thermostat is contained within the immersion heater assembly.

The thermostat mustn't be bypassed (shorted out) because the water would boil, potentially explosively, if the safety cut out failed.

Hi Gerry,
More than happy to be told othewise, but my understanding is that the heating element sits within the unit itself - it's the Santon PP120E.

The 'thermostats' I'm referring to are simply temperature gauges which switch the element on and off once the set temperature is reached. They are the Cotherm TRS 11″ T115 16A 250V.

What makes me think this is the guidance from the manual (in this case, for descaling the element):
"...Remove the thermostat by carefully pulling outwards from the immersion heater. Unscrew immersion heater backnut(s) and re-move immersion heater from the unit..."

I am unsure whether the thermostats act on independent (upper & lower) elements, or a single element.

I can't post links / pictures as I'm a new member but hopefully you'll see the parts I'm referring to via a quick google search.

Again, happy to be told I'm wrong, and learn something today!
Thanks

lohr500

If you don't need a full tank of water every day, then for now I would switch off the bottom element using the timer and leave the middle element switched on permanently with the thermostat set initially to 3.

This should help to reduce your electricity usage as you won't be heating the whole tank.

See how you get on with the middle thermostat set at 3 for a few days.

If you find you have plenty of hot water for your needs with just the middle heater working and it is hot enough, then turn the thermostat down to 2 and keep monitoring.

If you are running out of hot water, increase the middle thermostat setting to 4 or 5. This will raise the hot water temperature which will allow it to go further once you mix it with cold water for the shower, sinks,taps, etc. 

Longer term, get an electrician in to fit a timer to the upper immersion heater with a boost button. Something like this.

https://www.screwfix.com/p/greenbrook-t109-scr-analogue-dual-tariff-boost-timer/6415r

You can then set the timer to heat the water for a few hours before your main hot water usage each day. If you find you are occasionally running out before it heats up again next day, you can press the boost button to give it a quick boost. If it keeps running out on a frequent basis, then you can extend the timer interval, or even go for it being on 24 hours a day.

So long as you have enough hot water on tap running just with the middle heater, you can switch off the bottom one permanently!!

Hope this makes sense.

Gerry1

Wexi said:

Gerry1 said:

You seem to be saying 'thermostat' when you mean 'immersion heater'.  The thermostat is contained within the immersion heater assembly.

The thermostat mustn't be bypassed (shorted out) because the water would boil, potentially explosively, if the safety cut out failed.

Again, happy to be told I'm wrong, and learn something today!

No, I was wrong.  Most immersion heaters have the heating element and thermostat in the same assembly.  Looks much like your thermostat but a U-shaped rod.  I've learned something today !

Out of interest, how did you establish that the upper heater is always live?

Also, how are the rooms heated?

Wexi

lohr500 said:

Hope this makes sense.

That all makes perfect sense. Will test it out this way and see how I get on. 

Great shout in terms of getting the boost fixed and changed to a timer + boost. 

Thanks again!

Wexi

Gerry1 said:

Wexi said:

Gerry1 said:

You seem to be saying 'thermostat' when you mean 'immersion heater'.  The thermostat is contained within the immersion heater assembly.

The thermostat mustn't be bypassed (shorted out) because the water would boil, potentially explosively, if the safety cut out failed.

Again, happy to be told I'm wrong, and learn something today!

No, I was wrong.  Most immersion heaters have the heating element and thermostat in the same assembly.  Looks much like your thermostat but a U-shaped rod.  I've learned something today !

Out of interest, how did you establish that the upper heater is always live?

Also, how are the rooms heated?

Yeah after looking online I see what you mean - I seem be in the minority with this model.

I found out when I had a plumber around to fit the replacement thermostat. He told me the upper one was 'always live' - I thought he meant it could always be turned on via the boost, but I now realise he meant it's always On! 

Central heating (rads) is via a completely separate electric system - Heatrae Sadia Amptec Boiler C400. Thankfully I've had no issues with that in over 4 years. 

Cheers