Lack of hot water from an indirect cylinder system

[Lukewarm]

I have a well established oil-fired central heating system (installed about 30 years ago). The Trianco boiler has 2 water systems with 2 Grunfos pumps.
The hot water drawn from the 160 litre cylinder is not very hot although the radiator in the bathroom, on the same system, is hot.

I can feel the top pipe of the indirect coil on the cylinder is hot to touch, however the lower pipe is cold.

I have opened the bleed valve and removed the air, but the problem persists.

The immersion heater does heat the water up as a back-up but that's an additional expense.

I have checked that the pump is operating okay.
Does anyone have any suggestions or a series of checks to carry out.

[teach1376]

Have a look at the thermostat on the hot water cylinder first. If this is set too low the water will be diverted to the central heating before the cylinder contents get hot. Don't set it any higher than 65 C or there is a danger of scalding as the water at the top of the cylider is considerably hotter than that

[thedoctor]

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[potterton]

Have you solved your 'lukewarm' water problem yet?

I have a similar problem on a indirect boiler system. I notice that the hot water supply only warms up when the central heating is on. I also notice that adjusting the thermostat on the hot water tank has no effect on the boiler, ie. even when it is set to 80C the boiler does not cut in.

I think the relay controlled valve to the hot water system is working because I can hear it closing when I turn on-off the hot water via the controller. And because the water does warm up when the central heating comes on.

All of which leaves me confused as to what is the cause of the problem. Could it be the controller is failing to tell the boiler to start even thouigh the thermostat is working, OR, is the thermostat at fault?

Any ideas? :?