Hot water but no radiators

[S&M]

Hi

Long time reader but now need a bit of help that I can't resolve by searching.

I have a gas boiler (Ideal Classic RS40) with a Drayton LP722 timer. 3 way valve in airing cupboard along with hot water cylinder and central heating pump.

When the timer switches on for hot water the boiler fires up OK.

However, when the timer switches on for central heating the boiler does not fire up. The thermostat in the hall is turned up high enough.

If I then manually override the hot water and turn it on for 30 seconds and then off, the boiler remains on for the central heating and then continues to operate as expected i.e. cuts in and out as required by the thermostat.

I have just changed the motor in the in 3 way valve as various posts seemed to suggest this was the most likely cause. Didn't fix the problem.

Other things that it could be - Drayton timer, boiler itself, micro switch in 3 way valve controller etc............

Rather than just changing more parts does anyone have any suggestions as to what could be the problem?

Thanks

Mark

 

[Echo the husky]

Is 240V present at the hot water off wire (grey) of the 3 port valve when there is no demand for hot water?
Is 240V present at the central heating on wire (white) of the 3 port valve when there is call for heating?
Is this a new problem or has it always been like it?

 

[S&M]

I have 240V present when there is demand is for heating and also when there is demand for hot water.

This is a new problem - previously the heating would fire up the boiler without the hot water having to be on.

 

[Echo the husky]

I have 240V present when there is demand is for heating and also when there is demand for hot water.

At the correct terminals as described above and at the correct times? You need to measure this with a proper 2 wire voltage tester or multimeter set to AC volts. You can't use a neon screwdriver or similar as you will get false readings through the various resistors and other components in the valve head.

Does the valve motor move at all when anything is selected? With the the CH and HW on together does the valve close if the clylinder is up to temperature? (or the clyinder stat is turned down so that it clicks off)

Did you just replace just the valve motor or the entire valve head? If the motor is moving the valve to the correct position but not switching the boiler and pump on, there is either a problem with the switches in the valve head or the orange wire from the valve is not connected properly in the wiring center. Any photos of the wiring connections?

 

[chester24]

I used a multimeter.

I can hear the valve move when hot water is selected.

The valve closes when the hot water cylinder is up to temp.

I replaced just the valve motor with this http://www.screwfix.com/p/drayton-synchronous-motor/28670 - I'm suspecting I might have to change the complete valve actuator with one of these http://www.screwfix.com/p/drayton-mid-position-valve-actuator/40818

I noticed that there is a micro switch in the valve actuator - maybe this is faulty?

 

[MANDATE]

A faulty microswitch is highly likely. There are two in 3port mid position valve. Both have dual functions
No 1 supplies power to drive motor to mid position.The swich cuts off the power breaking the contacts but makes a second set of contacts, which provides power to drive the motor/valve from mid point to the CH position.
Faulty contacts could affect motor/valve movement up to mid point or after mid point.
No 2 is wired differently. Power is supplied to a PCB which is needed to hold valve at mid point through one pair of contacts. When this is no longer required, the power is diverted through the second pair of contacts and out of the valves orange wire.
When boiler involves hot water it is powered via the cylinder stat ,but with hot water satisfied or not turned on it has to to be powered from the valves orange wire.
If motor/valve does not move to CH position problem could motor, microswitchs or wiring
If motor/valve does move to CH position then microswitch No 2 is most likely the cause.

 

[Echo the husky]

If there is no power coming out of the orange wire in CH mode it will be the microswitch. If you are really handy you can replace the switch, but it is much easier to swap the whole actuator.

 

[chester24]

Thanks for all of the suggestions.

I'm going to try to get a new valve actuator today.

I'll post back with the results.