iBoost causing tank overflow?

zeupater

JimLad wrote: »

Found some on my phone from a few weeks ago before the iboost was installed. Looks like the tank is 150L and the immersion goes 1-5.

I did some googling of the model and it appears the numbers mean the following...

1 = 10°C, 2 = 25°C, 3 = 40°C, 4 = 55°C & 5 = 70°C

Would should I have it set at to optimise my free hot water but minimise danger?

Hi Jim

Realistically, 70C is starting to get on the dangerous side unless you have TMV protection on your taps ... effectively the time to severe burns from hot water isn't linear - at 50C it's around 1minute, 60C ~2seconds and 70C it's instantaneous ...not even enough time to swear and pull your hand away ... we operate our solar thermal above 70C, but that's with a whole house TMV in place - without one I'd be far more cautious ...

If the thermostat maximum setting is 70C you shouldn't really be getting that much additional water expansion that the pressure relief or temperature safety valve would open. My worry in the earlier posts is along the same lines as Hengus & piinks related to the accuracy of the thermostat. Do you have a (cooking ?) thermometer which can measure temperatures up to 100C ? - if so try to test the water temperature against the thermostat setting .... as it stands, it certainly sounds like a temperature/pressure related issue which, considering that there's a requirement to safety check a pressure cylinder annually, must either be related to turning the temperature up, or a component failing since the last service ...

HTH
Z

JimLad

zeupater wrote: »

Hi Jim

Realistically, 70C is starting to get on the dangerous side unless you have TMV protection on your taps ... effectively the time to severe burns from hot water isn't linear - at 50C it's around 1minute, 60C ~2seconds and 70C it's instantaneous ...not even enough time to swear and pull your hand away ... we operate our solar thermal above 70C, but that's with a whole house TMV in place - without one I'd be far more cautious ...

If the thermostat maximum setting is 70C you shouldn't really be getting that much additional water expansion that the pressure relief or temperature safety valve would open. My worry in the earlier posts is along the same lines as Hengus & piinks related to the accuracy of the thermostat. Do you have a (cooking ?) thermometer which can measure temperatures up to 100C ? - if so try to test the water temperature against the thermostat setting .... as it stands, it certainly sounds like a temperature/pressure related issue which, considering that there's a requirement to safety check a pressure cylinder annually, must either be related to turning the temperature up, or a component failing since the last service ...

HTH
Z

I have set it to 4 for the time being. I will source a thermometer and then wait for a sunny day to see how hot the water comes out.

Thanks for your help Z.

zeupater

evomatt wrote: »

I have mine set at 5 (70 deg) my kids are 8 and 9 and know the water comes out hot and to use the mixer tap. If the kids were younger id set it lower prob on number 4 to avoid scalding.
Also it looks like your stat is at the bottom of the tank so you'll be heating the whole tank (maximizing excess generation) im guessing your iboost will feed about 12kwh into it if youve used all the hot water the day before, then as you use the hot water during the day it will keep topping it up so you can easily feed 16kwh into it.
If youd fed 16kwh into it, not used any then the next day the iboost said it had put another 16kwh into it youve got a problem somewhere.

my kids cant wait till the summer as they can have warm water in the paddling pool instead of freezing cold hosepipe water

Hi

Again, let's look at Jim's 150litre cylinder setup. The immersion is said to be about 1/4 from the bottom, which suggests that it's installed above a GCH coil, so of the 150 litres only ~112litres can be heated by proportional diversion ... if the temperature is set to 70C (as stated) the temperature rise from 10C mains is 60C ... the thermal capacity of the cylinder from the immersion heater is therefore 7.8kWh (1.16*0.112*60), not a 12kWh guess ...

On an open forum it's really easy for people researching solar thermal or pv proportional diversion to allow their expectations of performance, savings and therefore payback to be a little optimistic, which the more unscrupulous section of the industry already exploit without assistance .... can we therefore look to continue this conversation, if necessary, when you've actually experienced pv for more than 4 winter months and had proportional diversion working properly for more than a few weeks.

HTH
Z

System

I have had a look at the manual for my unvented hot water cylinder. The immersion heater should have two thermostats built into it. The first (the one that you can control) is limited to 70C. The 'top stat' cannot be changed by the user and is usually set at about 80C: it's there for safety reasons. You need to check whether the water trickling into the plastic cone ( the Tuni Dish) is hot or cold. If it is cold, then your cylinder needs re-charging. If it is hot water, then one or both of your safety cut-outs has failed. The system needs to be checked by a plumber who is qualified/certified under GasSafe to work on unvented hot water systems. Put simply, do not take any risks with unvented hot water systems. They operate under pressure and tanks have been known to explode. Sorry to sound alarmist.

Rodders53

Hmmm.... When was this unvented cylinder last maintained and checked over? This sounds like a lack of expansion tank capacity due to loss of air pressure or failure of the expansion vessel bladder. This will result in a trickle of water out of the pressure relief valve into the tundish every time the water heats up.

The pressure vessel will have a Schrader tyre valve on it and (with the cold supply to the tank off, and the water pressure released by running hot water off) that air pressure should be checked annually at least...

It will typically, be preset to something like 2-3 bar ... if water escapes from the tyre valve then the pressure vessel bladder is shot.

Re-pressurising the vessel to the system design figure (usually marked on it by the original installer) will push water out of the open tap, and if the bladder is OK that should fix the problem. NB It's very hard work to re-pressurise by hand.

In theory a qualified installers need to change a faulty vessel. Some pressure vessels can be dismantled to have the bladder replaced.

Dig out the manuals for your installation (and/or look on the manufacturer's website for them).

evomatt

zeupater wrote: »

Hi

Again, let's look at Jim's 150litre cylinder setup. The immersion is said to be about 1/4 from the bottom, which suggests that it's installed above a GCH coil, so of the 150 litres only ~112litres can be heated by proportional diversion ... if the temperature is set to 70C (as stated) the temperature rise from 10C mains is 60C ... the thermal capacity of the cylinder from the immersion heater is therefore 7.8kWh (1.16*0.112*60), not a 12kWh guess ...

On an open forum it's really easy for people researching solar thermal or pv proportional diversion to allow their expectations of performance, savings and therefore payback to be a little optimistic, which the more unscrupulous section of the industry already exploit without assistance .... can we therefore look to continue this conversation, if necessary, when you've actually experienced pv for more than 4 winter months and had proportional diversion working properly for more than a few weeks.

HTH
Z

if the iboost put 7.8kwh into the tank then family have a couple of showers emptying the tank surely it could then put in another 7.8kwh already coming close to 16kwh?

Im only on my first winter so new to this and not mathematically minded i just accept that when the iboost says its put 16kwh into the tank for the days total that it is correct. I dont know how else to monitor it.
My immersion is half way up the tank and will take 4kwh before shut off then i only get 1 10 minute hot shower out of it and have to either wait for another 4kwh of pv heating or use gas to heat the tank up. Im thinking of either moving the immersion to the bottom of the tank or putting a second immersion heater at the bottom and using the iboosts second relay to power that one. Then i should have enough hot water most mornings for at least two showers.

Cardew

evomatt wrote: »

if the iboost put 7.8kwh into the tank then family have a couple of showers emptying the tank surely it could then put in another 7.8kwh already coming close to 16kwh?

Im only on my first winter so new to this and not mathematically minded i just accept that when the iboost says its put 16kwh into the tank for the days total that it is correct. I dont know how else to monitor it.
My immersion is half way up the tank and will take 4kwh before shut off then i only get 1 10 minute hot shower out of it and have to either wait for another 4kwh of pv heating or use gas to heat the tank up. Im thinking of either moving the immersion to the bottom of the tank or putting a second immersion heater at the bottom and using the iboosts second relay to power that one. Then i should have enough hot water most mornings for at least two showers.

4kWh input to tank only lasts 10 minutes??


Do you have a 'power shower' i.e. pumped water to the shower head. If not what is the rate of flow in litres/min.

Sterlingtimes

evomatt wrote: »

I'm thinking of either moving the immersion to the bottom of the tank or putting a second immersion heater at the bottom and using the iboosts second relay to power that one.

Carving a hole at the base of the tank sounds like a major exercise. Do plumbers have a tool to do this?

I had just had problems with my Mira Event manual power shower with the immersion thermostat set to maximum. I have reduced to 65 degrees to see what happens over the next few days. This has already reduced diversion to DHW. I am minded currently to think that iBoost is not greatly beneficial.

legoman62

You could cut an hole with a Hole Saw.....as long as the cylinder is in good condition. I've got a few, in various sizes:)

And fit one of these;)

http://www.toolstation.com/shop/Heating/d230/Central+Heating/sd2708/Essex+Flange/p41238

evomatt

Cardew wrote: »

4kWh input to tank only lasts 10 minutes??


Do you have a 'power shower' i.e. pumped water to the shower head. If not what is the rate of flow in litres/min.

Taken from south stafs water

1. a bath uses much more than a shower. A full bath uses up to 80 litres of water whereas a 5-minute normal shower uses about 35 litres, saving 45 litres of water. A 5-minute power shower uses about 60 litres, which still saves 20 litres of water when compared to a full bath

So a 10 minute shower would use about 70lt.

There is already a hole in the bottom of the tank which im guessing is there so you can put the immersion at the bottom of the tank.