Central Heating / Hot Water Issues

[Tortoise]

space.dandy,

Apologies, but do you have answers to the following:
1. When the tank has been heated, is the pipe out from the tank really hot - can you hold you hand on it, or does the heat force you to remove it?
2. Do you KNOW for CERTAIN that you're running out of hot water, or is it that the hot supply goes cold?

I've had roughly similar hot water issues, and NOT saying yours is the same but I've traced mine to a faulty shower control. I have separate temp & flow controls on the shower. Leaving the temp control in a particular position was (and still does!) allow the cold supply to flow into the hot feed, so all hot taps then flow with warm or cold water (rather than piping hot). Moving the control to a different position blocks off the cold supply or equalises the pressures between hot and cold, and all is well. The cause of the behaviour is one of the non-return valves (designed to prevent this very occurence) within the shower control isn't working properly, so need descaling or replacing. A common issue I'm informed.

If this description is in any way helpful, so be it, otherwise....I'll go back in my shell.

 

[Woody Alan]

"Tortoise" You make a good point. If the system has been installed correctly and the cold feed goes through the system pressure balancer to balance the hot and cold pressure this shouldn't happen as the two equal pressures should balance out, regardless of non return valve but that is not to say it's a perfect world and it is still worth looking at. Based on what you are saying it could also be the auto temperature control failing and will lean towards a cold failure over a hot for safety reasons. Also raises the point whether the cold has been equalised in pressure to the shower as it should be.

 

[mikej460]

And when you run a bath it just takes out the hot water all at once and the cold water that replace's it in the tank has little or no effect.

Two hours of heating the hot water before the showering start is probably insufficient time to heat all of the water in the tank, before you go changing things in the system try starting the hot water heating time a couple of hours earlier.

I think this is more likely the problem coupled perhaps with the heat loss through the pipes in winter and the tank not getting hot enough before switching to central heating. Take a look here at the reheat times for your cylinder
UNICYL | ThermaQ

 

[Terry - Somerset]

A properly working boiler should heat a typical domestic water tank in under 2 hours - possibly as little as 30 mins depending on size of boiler and tank, and whether central heating is competing with hot water.

First action shouold be to insulate the pipework from the boiler. In a cold loft there will be a significant heat loss from bare pipes. This will be greater depending on length of pipe runs.

If running a bath the first few litres will be cold, but as a bath of 70-100 litres is run in one go, thereafter the tap will seem permanently hot.

The flow rate in a shower is likely to be significantly less than running a bath unless you have a lot of power assistance. The means that at the start of any shower the heat loss is likely to be high.

Between one shower and the next the uninsulated pipes will cool down meaning that it will start cold. You will also have used the hottest water in the tank as the supply comes from the top.

This may not be the full answer - but it will certainly help.