Central Heating Problem - Randall 4033

[T13theobh]

Can anyone help please.

My central heating isn't working. The pilot light is on in the boiler (glow worm Space Saver). I can re-light the pilot no problem. I have a Randall 4033 Timer switch. When the hot water is switched on or in the timed period the boiler fires up (till today) but if I switch the heating switch to on nothing happens. After a few days if left on timed the heating has come on and seemed to work ok for a few days, maybe even a week but then out of the blue can stop working. Any ideas? Could it be the Randall 4033? Up till today the hot water was working, but now that has gone for a burden.

Any advice will be greatly appreciated.
Thanks in advance

 

[D_Hailsham]

Do you have any motorized valves? Like this: View media item 5945 View media item 5946

 

[T13theobh]

No I dont think so. I don't recognise those, where would they typically be located? The rad valves are the standard fair.

 

[D_Hailsham]

They are normally near the hot water cylinder.

If you don't have any valves, you probably have a pumped CH, gravity HW system.

Can you have the central heating on by itself or do you have to have the hot water on at the same time? If you have to have CH and HW on at the same time you will almost definitely have a pumped CH, gravity HW system. Another clue is that you have a pipe direct from the boiler to the HW cylinder, which does not go through the pump.

There are several switch combination (ON, OFF, timer) for the HW and CH switches. Have you check all combinations to see which ones work and which don't? It might be worth bypassing the timer to check the system works with the timer out of circuit.

If the timer is OK, the pump may be faulty. Turn power off and remove the silver screw in the centre of the pump (use a towel to catch the water which drips out) and the check you can turn the pump shaft with a screwdriver. Replace screw and turn power on. set the boiler to run and listen to the pump using a screwdriver as a stethoscope. You should hear it running. Check all speeds. When the boiler goes wrong, listen to the pump again.

 

[T13theobh]

Thanks for the reply.
The Heating and Hot Water are independant of each other. I can switch the HW on and the boiler will fire up. If i do the same for the heating, nothing happens. As I said, the heating is normally in the Timed position and has in the past worked after a few days of not working.

I don't feel comfortable about diverting the wiring from the timer but I will take a look at the pump as you have suggested. Come to think of it I think these is a valve near to the pump, so I'll take a look at that too.

Everything seems to be pointing to the timer switch but I know diddly squat.

 

[D_Hailsham]

Come to think of it I think there is a valve near to the pump, so I'll take a look at that too.

Everything seems to be pointing to the timer switch but I know diddly squat.

If there is a valve, like the RH picture above, then that could be causing the problem it can stick and there are switches inside which can go wrong.

 

[T13theobh]

I have checked and can confirm that I have a motorised valve V4073. Is there any way these things can be tested? or is it a case of simply replacing the unit?

 

[D_Hailsham]

I have checked and can confirm that I have a motorised valve V4073. Is there any way these things can be tested? or is it a case of simply replacing the unit?

We're getting there.

Yes they can be tested.

A quick explanation: Water enters the V4073 in the branch labelled AB and exits the two side branches. One branch (labelled B) goes to the HW cylinder and other (marked A ) to the radiators. The actuator (box on top) can set the valve to three positions: B open; A open; A and B open. When the valve is not energised it sits in the B open position.

The first thing to check is that the valve is not sticking: Turn of the power to the system. Move the lever on the side from Auto to MAN. You should feel resistance as you are opening the A port against a spring. When you release the lever, it should move back to Auto. If the lever moves easily from Auto to Man, the valve is stuck. Remove the actuator (box on top - no water will come out) to expose the valve spindle. Try turning this with a pair of pliers - it only turns through about 20 degrees, not a complete rotation. If it is stiff it may be possible to free it using a very small amount of WD40 or a silicon spray). Replace actuator and check again. If it is so stiff that the valve does not move easily using the lever you will have to replace the complete valve.

If the valve is not sticking, we need to check the electrics.

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

There is a five core cable connected to the valve. What is the other end connected to? A picture might help - with the lid of any box removed, if possible. I can then give you specific testing instructions.

 

[T13theobh]

Cheers, I'll check this out. I noticed the little lever and it moves very easily so I guess the valve is stuck. I'm not that comfortable with electrics but the brother-in-law is a sparky so will ask him if we need to go down that route. I'll let you know.

Thanks again