central heating not working unless hot water turned up All aspects of plumbing questions and answers, help, tips and information

[lozzer44]

hi hope someone can help me with a problem ive got since needing heating this autumn,when i switch the boiler to hot water & central heating the only way i can get the radiators to warm up is to turn the thermostat on the hot water cylinder up,as i turn this up i can hear the boiler kick in & the radiators then get hot,but i end with the cylinder thermostat at 70degs.If anyone can come with any ideas i would be very grateful

[Steve the gas]

Hi Lozzer,

Need more info on sysyem and set up please.

If gravity - sounds like motorised valve problem.


Hth

[lozzer44]

Hi Steve

how would i know wether the system is gravity fed?

i can tell you it has a pump & a 3 way valve & our house is a bungalow (not sure that makes any difference)

should i be able to see/hear the valve move when changing from HW to HW & CH

[lozzer44]

Hi Steve
How would i know if it is gravity system?

i think it may be the valve,it does not seem to move or make any kind of noise when changing from HW to HW & CH

The pump seems to be working fine

[chris_on_tour2002]

if it is gravity fed then you will have a small "F&E" (feed and expansion) tank in the loft, usually directly above the boiler. you might have a cold water storage tank in the loft as well - this will be the big one, the smaller tank will be your heating feed tank.

if no tanks then its probably a pressurised system and there will be a pressure gauge on or near the boiler.

[objectiser]

Hi

I am having the same problem - I believe mine is a gravity system. The thermostat in the hall still clicks when turned up, which seems to suggest that it is still working, but it does not trigger the boiler.

As with lozzer44, the heating only comes on when the hot water tank is switched on, and the termonstat on the hot water tank is high enough.

Any help appreciated.

Regards
Gary

[nitro23456]

definately motorised valve in my opinion. it should move between all 3 position as an when the different sources of heat are required.

To test it you can allow the whole system and house to cool down by turning off system. Then turn your room temp stat to higher than ambient (say 25 celcius for testing purposed) and your cylinder stat to below what you think you stored water is still at...... ie if you think it should still be at 50 celcius from previously heating, turn it down to say 20 celcius.

turn the system back on and the valve should move to CH only as your room will be below the 25 celcius mentioned above but your water should still have held its heat above the 20 celcius stated. You can then turn you water back up to say 70 on the stat and the motorised valve should move to HW or both CH/HW.

Hope that makes sense!!

[objectiser]

I tried tests as you suggested. When the system was turned on with just the room temp stat set to 30, and hot water temp set to 20, there was no reaction - no motor sound.

When the hot water cylinder temp was turned up, it triggered the heating and the motor activated.

There also seemed to be motor activity when the CH button was turned off and on, with the HW already being on, but again no motor activity when both CH and HW on, and then the HW turned off.

Not sure if this leads to any conclusion about the motor, apart from it seems that the room termostat is not triggering it.

BTW - the motor unit does not have an indicator related to HW, CH and HW+CH, but can hear internal movement of what would appear to be a mechanism switch. The only external lever that moves is between two settings AUTO and MANUAL. But this tends to stay in the AUTO position.

I have also tried resetting the controller unit, but that had no effect.

Any further thoughts?

Regards
Gary

[Steve the gas]

As a temp fix, keep the lever in the manual position- you may have to bend it slightly to keep it there.
If this works the head needs replacing or poss the whole MV.


Hth