Oso Unvented Hotwater Cylinder

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Hello All, I have been in my new build house for 20 months now with a 125 litre capacity Oso Unvented Hotwater Cylinder. I have never really noticed a problem with a lack of hot water when i have needed it, but in the last few weeks the amount of hot water available has seemed a bit of a lottery! I have an 8 month old son, who my wife and i bathe every night. Some nights we have a nice deep bath (6-7 inches) with the amount of hot water available and other nights we get 1-2 inches in the bath before cold water starts coming out the hot tap.

There is no obvious rhyme or reason to this as our washing machine and dishwasher only use cold water feeds and nothing else in the house requires hot water. We have started leaving the thermostats hot water setting on constant but it has made no difference. Can anyone please advise me as to whether im doing something wrong or missing something? Thank you.....
 
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What setting is the thermostat on the tank set to?

Are you in a hard water area?

Are the flow and returns to the cylinder hot?


Essentially, is the tank heating fully?
 
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Hello Dan, Thanks for your reply. I am not technically gifted in any way shape or form and so the short answer to your questions are that i don't know! Im sorry! I also have no manual for this cylinder either, i have never seen one. I guess the builders forgot to give it to me when they sold me the house.

I can't see a thermostat on the cylinder itself?

I live in Launceston, Cornwall and to the best of my knowledge the water is not hard here.

How would I ascertain whether the flow and return is hot?
 
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Do we assume that a boiler is heating the cylinder, or is it a direct model on E7 electric?
 
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The thermostat is behind the white panel at the bottom - careful there is mains electrickery in there.

If you want a manual send me an email. We fit loads of these tanks and they are excellent.

When you expose the thermostat, and when the system has been heating the tank for say 45minutes, you should check the temperature of the tank by feeling the skin next to the thermostat - if you have a contact thermometer even better - again watch for electricity.

If the tank is hot, then you have a problem of volume.

There are ways around that but you will need a G3 registered plumber with a brain.
 
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Some nights we have a nice deep bath (6-7 inches) with the amount of hot water available and other nights we get 1-2 inches in the bath before cold water starts coming out the hot tap.


Have the pump checked on the secondary return.
 
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Right, i have taken that panel off. Both the temperature controls on the cylinder say 60 degrees celsius..... The metal skin immediately next to those dials is very hot. Sadly, i have no accurate thermometer to hand.

Incidently, the cylinder does heat from the boiler downstairs, not economy 7....
 
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Well in that case you have 125 litres of hot water...

Now run Mrs Dawson a nice hot bath - as deep as you like... She'll thinks its Christmas- or her birthday...

But we all know that secretly you are testing the reheat of the tank. Run the bugger cold.

Now run the boiler to heat the tank up (make sure you boiler thermostat is set to 75% or thereabouts. The coils in these tanks like a flow temperature of 75 to 80 degrees.

Now time the reheat of the cylinder. It should be 28 minutes.

Repeat test for yourself.

Also check the safety discharge pipe to make sure you are not loosing water through there - it could be that the internal air bubble has gone and you are loosing hot water that way...
 
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The maximum the dial on my boiler downstairs can be adjusted to is about 50%? The graphic above it gives the impression it should be able to adjust further, but i can't turn it anymore.

Where is the safety discharge pipe? Is that the one on the right hand side of the cylinder quite near the top as i look at it?
 
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Right, i ran the water til it got cold and the metal skin was cold to touch. 28 mins later, the cylinder skin was hot to the touch and the bath ran about 4 inches (ran hot for about 3 mins) hot, then went cold again....
 
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Was water coming through the safety pipe?

Had the cylinders zone valve closed 9telling you the tank was at full temperature? Remember "hot to the touch" is only around 49 degrees.

It makes quite a difference.

The human body is great at sensing temperature, but is poor at accurately gauging it.
 
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;) er.

The zone valve should be on the flow pipe is just to the left of the panel - it should have a sticker saying Flow.

The valve is normally a silver box with a black fly lead. Under the lead is a little lever - when the valve is open (heating the tank) the lever is loose and flappy. When the tank is fully heated the valve springs closed and the lever goes stiff.

Only when it is stiff (with the clock call for heat) is the tank up to temperature. I am not familiar with your boiler but I see no reason to not turn the thermostat up to almost maximum - the temperature range is 65 - 80 degrees.

If the tank is fully heated you should have enough to fill the bath and have a bit left over. Unless you have a huge bath.
 
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I didn't even see your first post, i was too busy running up and down the stairs following Dan's advice! Im sorry for not seeing it. Still not sure i particularly deserved that reaction though... Im a Management Consultant not a plumber/boiler engineer/Unvented Hotwater Cylinder Installer!
 
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