Leak in hot water cylinder heating coil?

[haywardave]

Hi guys
Over the past couple of weeks I have had to top up the pressure in my hot water/central heating system every 3-4 days. I have access to most of the pipe work in the house and can find no evidence of a leak anywhere. I have bled the radiators. I would guess that I have to let the water into the expansion vessel for about 30 seconds each time. The boiler was installed in the cellar around 1980 and origanally was fed from a header tank in the loft. Around 15 years ago I replaced the header tank with an expansion vessel which is sited beside the boiler. There is no evidence of any water coming from the expansion vessel vent.
My guess is that there is a leak in the heating coil in the hot water cylinder, if this is the case how can I prove it?
I am thinking that if I turn off the cold head to the hot cylinder and turn on the hot taps I should have a slow flow and loose pressure from the expansion vessel. What do you guys think.
Thanks in advance.
haywardave

 

[twgas]

Your method would take some time to prove anything, better to disconnect the cylinder flow and return then see if pressure still drops,
Incidently, what boiler and type of system do you have?

 

[Terrywookfit]

I bet it has no o/h stat.

 

[twgas]

I bet it has no o/h stat.

I was trying to be subtle.

 

[haywardave]

Mick
The boiler is a gas Clyde 045/5 installed in Feb. 1980. It is a pressurised system with a red expansion vessel which usually hold it's pressure fine at just over 1 bar from memory. It runs both the heating (15 rads) and hot water controlled by a timer and a couple of valves. Hope this answers your questions.
Regards
haywardave

 

[haywardave]

The system has an over heat stat on the side of the tank, frost protection stat, over pressure and under pressure switches close to the boiler in the cellar.
haywardave

 

[twgas]

The system has an over heat stat on the side of the tank, frost protection stat, over pressure and under pressure switches close to the boiler in the cellar.
haywardave

If you mean the cylinder, that is NOT an overheat 'stat.

 

[haywardave]

The hot water cylinder has a thermosat strapped to the side and the boiler has a factory fitted limit thermosat which the instruction book states is preset to oprate at 95'C and a thermostat that controls the output temp to a maximum of 82'C.
I guess this has nothing to do with the loss of pressure from the system.
haywardave

 

[twgas]

I guess this has nothing to do with the loss of pressure from the system.

No