hot water but wont stay hot.

[FRANKIEJUNIOR]

I cant understand why when i put the heating on for a couple of hours,the next morning the water is cold. I have a firebird 90 oil fired boiler sealed central heating system, with an indirect hot water cylinder. I couldnt see any flow and return pipes from the boiler to the side of the cylinder but i did see 2 15 mm pipes going into the top of the cylinder. Ive found out that this is a conversion kit from a direct cylinder to an indirect one in the 1970s. Would this have an effect on why its notholding hot water.
There is enough hot water to fill a bath immediately after the heating but wont store it. Also the willis immersion heater only provides enough hot water to fill a basin no matter how long its on. There are no motorised valves are anything like that. There was a back boiler at one stage but its discnnected. Thankyou.

 

[namsag]

Do any of your pipes to the hot taps go under concrete floors or suspended floor downstairs as they may have a leak in them and the hot is draining away to be replaced by cold water.
You could try tying up the ball valve to see if water level drops in tank over a period of time

 

[kevplumb]

the cylinder is of course lagged

 

[doitall]

Is the pump turning off.

Did it used to store it before.