Megaflow - insufficient hot water amount

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I have an issue with a Megaflow direct unvented hot water cylinder with the lower immersion heater powered by economy 7 and the upper one by a limited time booster switch. The booster was rarely required. It was operating satisfactorily up until I had a shower valve replaced. Since then it runs out of hot water after only a couple of showers. I have had an electrician check out the immersion heaters and they are both good. I have replaced the thermostat in the lower immersion heater but with no effect. The 2hr boost does not seem to produce much hot water. I have had the lower immersion heater wired into the day rate power supply and left on continuously. Although slightly improved it still runs out of hot water prematurely. Any ideas please?
 
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Have you tried using both immersions? Is it a new cartridge valve or whole unit?
 
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Yes. We have tried both immersions at the same time. No difference. The entire shower valve (hydramax) was replaced. Does this help?
 

snb

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how big is the cylinder? and how long are you showering for?

some of the newer showers can use 18 to 20lt/min water. the drencher types can be nearer 25lt/min so a 200lt cylinder with a mix of hot and cold would only last 15mins or so Max. people are always in a shower longer than they realise
 
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Hi SNB
Thanks for your response which does seem to fit the symptoms

It's a 170 litre tank so at the sort of flow rates you mentioned it would only last a short time. I have checked that the shower head is set to its economy setting but could I adjust the flow rate further by introducing valves on both hot and cold feeds?
 
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Hi SNB
Thanks for your response which does seem to fit the symptoms

It's a 170 litre tank so at the sort of flow rates you mentioned it would only last a short time. I have checked that the shower head is set to its economy setting but could I adjust the flow rate further by introducing valves on both hot and cold feeds?
Does your shower not have a valve to control the delivery volume? Or are we talking teenagers who will ignore instructions about running it at half...

I'd get that bottom heater back on E7 fairly sharp if I were you, your next electricity bill could be a bit steep. If the BOOST heater runs for an hour at 3kw it should heat the top half of the cylinder more tahn adequately.
 
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Actually we are talking tenants so useage not directly under my control. I will get the bottom heater back on promptly. Can immersion heaters partly lose their heating ability? I always thought that it was all or nothing with them.

The tank has 170 litre capacity if that helps.
 

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