CH only working when HW turned on.

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Hiya all.

Nervous first-time newbie with a question.

Hope someone can help......

Over the past few months the heat output of my homes radiators have gradually deteriorated. I have bled and rebalanced all the radiators to no avail. It improved heat for a while but only at the expense of other rads in the house. Gradually all heat to the downstairs radiators stopped and in the past few days the upstairs radiators have packed up too.

The Potterton Netaheat boiler comes on when the CH is requested but only works for around 5-10 minutes before turning itself off again and obviously cannot be heating sufficient water to warm the radiators properly. When the hot water only is on the boiler works fine, staying on as it should and producing loads of hot water.

My system has two 2 way motorised valves. One is on the hot water pipe from the boiler leading to the cylinder and the other appears to control all hot water to the CH system itself. Both appear to be working. When I turn the room CH thermostat down the CH motorised valve appears to engage and becomes rigid indicating to me that it is performing its function.

Thinking the problem was probably the pump I replaced the ageing pump with a new one (even installing it the right way round!!). On advice I also changed the boiler stat. Neither the change in pump nor stat has had any effect whatsoever. All radiators are still freezing apart from the first one in the loop which is only luke warm.

Despite my best efforts my problem remains.

The only way I have discovered to get any heat in the house is to turn on the CH and HW at the same time and after 3 hours the rads finally do get properly hot as they should.

Any ideas ?

Any advice would be greatly appreciated.

Cheers

Elephant Guy
 
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There is a micro-switch in the CH 2-way motorised valve that should close as the valve opens, to supply 240 Volts to the boiler and pump. Either this switch is faulty or there's a break in the wire from it to the boiler.

If it is the switch that has failed, then you may be able to just replace the motorised head of the valve (if the head is detachable) - without draining the system.
 
Thanks CH4.

The 2 way motorised valve is made by Tower. I changed the motor about 6 months ago. Would changing the head be difficult? Or possible? The motor seems to engage when the room stat is turned down though.

Any further thoughts appreciated.
 

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