No Heat in Radiators

[sandyzoo]

Hi,
I wonder if someone could offer me some advice regarding my central heating system?
Everything was working fine up until about a week ago. Suddenly one evening, I noticed that there was hot water, but no heat to the radiators. It was very cold, and it was a week before Xmas, and I have guests coming!!

I am no expert with these things, but did some investigation.

1) The pump is turning
2) The room thermostat is sending a signal to the junction box in the airing cupboard
3) The boiler does fire up - but only until the water is hot

After reading posts on this forum, and others, I focused on the motorised valve. It looked ancient. I put the switch in manual position, and hey presto - heat!! But only until the water is hot, then it cuts off again.

Ok I thought - and bought a new actuator head. However, sadly after this was installed the behaviour is the same. Hot water - yes. Heating no (well actually I do now get heating int he upstairs radiators while the water is heating up, but to get heating in the downstairs ones I need to put the actuator on manual).

I turned the cyclinder thermostat up, to see if this had an effect. This kicked the heating back into life, and the radiators stayed on for quite a lot longer - long enough to heat the house. But the hot water will now melt the skin off you... so not an ideal situation

So I find myself wondering what the fault could be. Could it be the control box sending only the Hot Water signal? Is the motorised valve not turning enough under the power of the motor, and so not sending the "fire up!" signal to the boiler?

I'd appreciate any advice.

I have an ex council house with an old back boiler. The airing cupboard upstairs has a hot water cylinder, a randall control unit and the pump.

Paul

 

[sandyzoo]

Someone has not helpfully advised me that it could be the actual motorised valve, rather than the actuator head that was the problem.

I have ordered a repalcement, but in the meantime.... over Christmas...

Is it possible to "force" the valve open in fully working order? I never heat the water without heating anyway.
When I have the actuator on "Manual" I get heating but only until the water is hot. Is it possible to open the valve in such a way as the rads work on the room thermostat (rather then the hot water temperature)? I guess I don't understand what sends the signal to the heating system to fire up for heating once the water is hot

 

[dcawkwell]

Someone has not helpfully advised me that it could be the actual motorised valve, rather than the actuator head that was the problem.

I have ordered a repalcement, but in the meantime.... over Christmas...

Is it possible to "force" the valve open in fully working order? I never heat the water without heating anyway.
When I have it on "Manual" I get heating but only until the water is hot. Is it possible to open the valve in such a way as the rads work on the room thermostat (rather then the hot water temperature)? I guess I don't understand what sends the signal to the heating system to fire up for heating once the water is hot

Use the manual latch on the side of the diverter valve to open the valve.
It will then stay open. Set the tank thermostat on the tank to its highest setting about 90 degrees. On the boiler turn the temperature down to between low and medium.
The hot water tank will never get to it's temperature and keep the boiler running. Because the valve is open it will be give hot water and central heating.

 

[mogget]

Do you have a multimeter and know how to use it?

Edit: crossed posts again.

 

[footprints]

Diagnosing faults on three port valves can be a nightmare there are so many things that can be at fault and stop the valve from operating.
It can be a fault on the off wire from the cylinder stat or the programmer, it may be the room stat not calling for heat the list goes on…………
Does the actuator head motor over if it is removed from the valve? If it does it might be the valve spindle is too stiff in which case a new complete valve will solve it,
you might even be able to work it back and forth to free it temp.
If not I’m afraid the fault is elsewhere and unless you are good at wiring it needs an engineer .

 

[sandyzoo]

Thanks for the replies.
I have turned the cylinder stat up. (I hadn't lowered the boiler temperature one... I am not sure what that actually does!)
I do have a multimeter, and I'm not afraid to use it.

In addition, I can confirm that *some* sort of signal gets to the valve, because I can feel the difference int he area of resistance on the manual switch. If the heating is set to Water only, then I have to push quite hard to get the switch in Manual.. but if it is on CH + HW, then the switch pushes into manual very easily.

 

[mogget]

Given what you've said about the lever resistance, I think the valve body itself is probably getting stiff like footprints said. Application of some WD40 to the spindle might keep it going over christmas.

See if this page helps to check out the electrical side: http://octaveblue.co.uk/c_heating/

Bear in mind that some boilers have the pump fed directly from them for pump overrun. These boilers also require a permanent live.

Also bear in mind that the connections in your junction box may not necessarily be in the same order as shown on the diagram!

Y plan is for one 3-port valve

S plan is for 2x 2 port valves.

 

[sandyzoo]

Thanks very much!
Those wiring diagrams are most excellent. So I'm guessing I am going to find a lack of power on the orange wire from my Diverter Valve when the hot water is up to temperature, regardless of room thermostat setting.
I will check it out later.

 

[mogget]

Just as a point of pedantry, a diverter valve and a mid-position valve are both 3-port valves but they are different in operation. A diverter has only 3 wires, a mid-position 5 wires. Most likely you have a mid-position valve which can send water to HW and rads at the same time, unlike a diverter.

If everything is working properly, the orange wire should become live whenever the boiler should be heating the water. But this depends on the valve being able to move to the correct position to switch the current, and if the spindle is stiff this might not happen.

If you are getting the correct voltages at the grey and white wires (depending on stats and programmer) it is likely that the valve body has failed, given that you have changed the actuator.

Work through the diagrams and you should have your answer.

Hope you manage to get your heating on for christmas!

 

[sandyzoo]

Thank you!
I have some heating now, by turning the cylinder stat UP and the boiler controls DOWN.
I think any further steps will be taken after Christmas!!

thanks for all the advice.