I have a gravity fed system, the hot water only works when we have it set on ch an hw, whats wrong?

Question

Gravity fed system! hot water works only when its set on ch and hw but when its on hot water only it doesnt heat up, can any1 help?

Answer 1

Check that there is water in your header tank

Answer 2

What more do you need than CH and HW.Central heating and hot water.

Answer 3

We have this problem also, I just turn all the radiators off in the summer.....

Answer 4

You have 2 motorised valves in your system. One for hot water and another fot your central heating. When you presss your programmer for hot water. The one for your hot water is not opening, most probably the little motor has faile. To buy a new valve is about £40/50. I you turn the boiler electrics off and remove the valve cover, you can change it yourself.  

Answer 5

motorised valve stuck in HW/CH position

Answer 6

you got air on top of the coil  

Answer 7

Start by watching the motorised valves to see which one works and when. If both valves open and shut, then you probably have a faulty programmer.

Answer 8

Sounds like you've got the wrong type of controller fitted.  With a gravity fed system, the water gets hot whenever the boiler's on.  The radiators get hot when the pump comes on.

Answer 9

If the hot water circuit works through gravity and the heating circuit is pumped then it could be a partial blockage or air in the HW circuit.When the heating comes on the pump will aid the flow around the hot water coil because of a thing called an injector tee.

First thing to check is that there is plenty of water in the system,then check for sludge in the pipework.

If the system has two motorised valves then the end switch in the HW valve is not bringing the pump and boiler on,they are only being activated by the CH zone valve.

Best bet is to phone a local heating engineer.

When you say gravity fed,do you mean fed from a tank in the attic or the HW circuit has 28mm flows and returns that heat through gravity?

On a gravity system the open vent should be connected to the highest point on the primary flow,but air can get trapped at the connection onto the coil,it should have a brass fitting,slacken it several turns,if there is any air the water pressure should push it out.Tighten the connection then repeat several times to make sure.

Gravity systems are old,unless its solid fuel,and it probably needs a chemical flush.

Answer 10

If it's 28 mm Gravity fed then they will be no motorised valves on the hot water side the most likey cause is an air lock in the coil