Hot water only heating when heating also on???

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Hi all,

I have a Bosch Greenstar system boiler with a ariston pressurised cylinder and been having an issue with my heating system for some time. Its been going on so long that i cant remember when it started. I had a potterton boiler before and that also had the same issue so it cant been the boiler.

I need to have the Heating on to enable the heating of the hot water tank.

On the programmer if i click on the "hour" button for heating the light comes on and the boiler fires up for and hour and heats the house. Howerver If i click on "hour" button for the water the light comes on and nothing happens, the boiler does no ignite? Therefore the only way to get hot water is to have the heating and water on together.

Would say this is not to pleasent in the summer however the rasiators have thermostats on so not been an issue until this week when now the hot water does not seem to be heating even though both lights for water and heating are on.

Can someone advise what the issue is likely to be so i can get the appropriate person in?

Electrical fault - Wiring issue? programmer not wired up right? Has no been touched?

Motorised valve issue? - How do i check they are working - i have two of them next to the cylinder in the loft? How do i know which one does what?

Many Thanks

Ian
 
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When you say that the wiring has not been touched, do you mean that that it has not been touched since the old boiler taken out and new one fitted.

What controls do you have make and model etc.

It definitely sounds like a wiring fault somewhere.

Graham
 
Hi Graham, thanks for the reply

Its a honeywell ST6200C controller. I had the same controller with the old potterton boiler. I had an extension built and the controller was moved from the original position to the outside wall which is no in the new extension. So effectively moved 1 foot. thats what i meant by the wiring not touched. Obviously the new boiler needed to be wired in.

When the new boiler was put in by the builder nothing was touched in the loft or on the programmer side. this problem has been happening i would say for at least 5 years. thanks
 
It could be anything as we dont know if it ever worked.

But if it did then its likely to be a fault in the HW motor valve.

To diagnose needs someone able to use a test meter or a competent heating engineer.

Tony
 
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thanks Tony, I have a mate thats an electician. I will try and get him around to test the motors with a multimeter.

I just did a test someone receommended by switching on the heating for one hour on programmer (obviously boiler does nothing) and checked both motorised valves and moving the manual levers does not kick the boiler in and they are not floppy, you hear the motors turn and the lever fall back to their original postition. does this point to a wiring issue? thanks
 
I think that you are implying the HW motor is not powering. Might be open circuit.

Electricians are usually not very good with heating controls.

There are also microswitches in the head.

Moving the lever does not usually bring on the boiler but only opens the valve.

Tony
 
Thanks again Tony,

So what does control the boiler when i switch on from the controller?

I have turned on the Heating only and the 1st valve goes loose so assuming that is working fine.

what does the microswitch do? Just engage the valve motor? or is the other way around the motor engages the mocroswitch?

I have moved the 2nd valve to manual and locked in postion and now the water is beaing heated again? The lever moves with no minimal effort and you can hear the noise of the motor so would assume the valve is not stuck.

thanks Ian
 
It could be the hw valve is opening but not switching on the boiler, when you turn on the heating the ch valve is opening and the micro switch is firing the boiler, because the hw valve is already open your cylinder will heat up, it could be as simple as a loose wire or a knackered m/switch in the hw valve.
 
Thanks Picasso

I will replace the microswitch followed by the motor and if that fails will get in a heating engineer to look at it.
 
Your motor was not opening the valve but its not seized as you hear it being turned when you move the lever.

The obvious cloclusion is that EITHER a supply is not getting to the motor OR the motor is not working because its open circuit.

You need to TEST the resistance of the motor winding, it should be about 2000 ohms but its probably O/C.

Its most likely to be the motor failed.

Tony
 
Thanks once again tony.

Some further details after some weekend testing:

I have swapped over the motor and still the same issue. I got a friend to switch on the boiler whilst i was in the loft and noted the following:

When we switch the heating on the you can hear the motor on the valve and the lever slowly moves from left to right. The lever is then floppy and I was told the boiler kicks in downstairs so all well. When the boiler is switched off the lever falls back left.

When we switch the hot water on you can hear the motor on the valve move however the lever does not move left to right altough it does go floppy and the boiler does not start.

As i have replaced the valve motor would this now point to the microswitch being at fault or again would i need to test this and where is the best place to purchase on and are they easy to change? or shouldii just replace the whole head? Thanks Ian
 

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