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I have a baxi 105e a I have hot water but no heating this as been on going for months got British Gas out 1 off payment changed pcb and sensor still wouldn't work he said needed power flush £600 rads were very old so got nephew who is a plumber to change pipe work and rads the boiler works fine for hot water but when you switch to central heating the boiler temp neons go right to the top temp very quickly then shut off temp drops again and boiler fires back up but again very quickly the feed pipe is very hot but the return pipe cold and rads do not heat up any ideas what this could be thankyou

get the Plumber back ,and get him to check circulating pump is working correctly

gas engineer said pump was fine and plumber said pump appeared to be working fine

If the temperature neons light up quickly then the water is not getting away from the boiler fast enough. This can be caused by the diverter diverting the heat through the plate heat-ex rather than the heating flow the hot water will heat quickly as there are no taps open and the heat can't go anywhere and this will cut the boiler off as it would have reached temperature. Or there could be a blockage in the main heat exchanger or pipework.

Turn off boiler so that it wont come on for water or heating. Run the hot tap so that there's no heat left in the hot water pipes, then turn off tap.

Turn the boiler on for central heating only - feel the hot water draw off pipe - if this gets hot then the diverter is stuck.

If the hot water pipe remains cold - the diverter should be ok.

This means there could be a blockage in the pipework or the main heat-exchanger - you could have this removed and cleaned out. (are you 100% sure the central heating temperature sensor was changed ?)

Hope this helps

My boiler has hot water and hot water+central heating together so how do I choose central heating only and which is the hot water draw off pipe thanks for your help the guy who originally fitted the boiler said he fits them but does't repair them

figured out which was hot water draw off pipe when I did what you suggested I turned hot water dail to zero and switched central heating on the feed pipe was red hot but the water draw off pipe remained cold. The gas engineer showed me the sensor but I am none the wiser if it was changed. If it is the heat exchanger is it an expensive job thinking of just giving up on it and getting a new boiler. Thanks for your help ,you don't happen to do repairs in the cumbria area(only joking).

It's a combi boiler - you only heat the hot water when you open a hot tap, it gives you the option of Central Heating and Water for the winter. And Hot Water only for the summer.

Turn the selector switch to CH & HW, as long as all taps are closed - onlt the central heating will be on.

The hot water draw off is the second pipe from the left.

had this exact problem. The solution was the pump was airlocked,remedied by unscrewing large silver screw on pump to let air out.the return CH pipe became hot within minutes