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I have a vented central heating system with 15 radiators. I have had to balance the system with the radiators nearest to the boiler and pump almost locked off completly to ensure that flow reaches the furthest radiator. The problem now is that even though the radiators do get hot (eventually) the return flow is always luke warm therefore the bolier is always fired up heating the water.

If the boiler is purely heating the hot water tank the boiler operated as expected. Fireing every 5 / 10 mins or so.

I have powerflushed the system and that has not helped

Any advice?

New Pump - If so what size? 15/50 or 15/60
Still not balanced properly? - If so how can I ensure flow gets to the end radiator - Furtherest radiator is about 12metres away from pump

Thanks Rich

RichD wrote:The problem now is that even though the radiators do get hot (eventually) the return flow is always luke warm therefore the bolier is always fired up heating the water.

If the boiler is purely heating the hot water tank the boiler operated as expected. Fireing every 5 / 10 mins or so.

Everything you mention points towards the boiler capacity being unable to cope with the output of the radiators. The return temperature should always be lower than the feed temp anyway, so that doesn't actually help much. More importantly, what is the feed temp like?? It must be substantially warmer than the return temp.

If the boiler is firing continually without rest or reaching temperature, then it is being asked to achieve over 100% capacity.

The fact the boiler fires normally when heating the hot water only bears this diagnosis out too.

Get your boiler serviced and ask engineer to check the burner pressure (he should anyway), maybe boiler is under performing or boiler may be inadequate for heating load if radiators have been added to system or boiler undersized.