DIY Doctor

Pumped / vented system, no hot water from indirect tank

Postby p_j_smith » Thu Jan 10, 2008 8:52 pm


I moved into a house approx 6 months ago, and ever since the hot water has never been great, after 2 weeks with the heating / water on for 2 hours a day (away on holiday) the hot water has really gone down hill.

System Spec:
Non condensing boiler
Vented / Fully pumped system
Indirect heating of hot water
All radiators separate thermostatic valves
Electronic control of radiators / hot water via 3 way valve
Thermostatic control on hot water tank
Pressure relief in system set at 1m / 1.5m of head pressure

The pump works fine

The 3 way valve seems to work fine as it directs the flow either to the radiators or hot water tank dependent on electronic controller, I felt the pipes heat up when the signal was sent to the valve.

The problem seems to be when I allow the hot water supply from the boiler to go to the hot water tank, the inlet pipe gets hot, however the outlet pipe only gets slightly warm, and the hot water from the taps again is only slightly warm too.

Does anyone have any idea about this, could the heat exchanger in the tank be blocked, or should the system pressure be raised to force the water thru the heat exchanger?

I've seen an old post saying about an air lock, I'll try the fix to see if this helps.

Any help gratefully received.

Thanks, Peter
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Simply Build It

Postby marrtin » Fri Jan 11, 2008 9:02 am

The heat exchanger is often the highest point on the water circuit, and often air can become trapped consequently restricting the flow of water through the coil.

Usually, there is a valve similar to a radiator bleed screw fitted into the end of a short length of vertical pipe between the motorised valve and the tank coil. Release the valve and vent any trapped air.
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