Boiler not firing up

[YellowPlanet]

Hi there,

Hopefully someone will be able to help me out with this CH/HW system.

I don't know what my stsem is called. It's not a combi though.

The components are:- Potterton Boiler, Potterton Controller, Grundfo Super Selectric Pump, Honeywell v4073a motorised valve and a honeywel room thermostat.

The pilot light is still on in the boiler but I can't get it to fir up. I thought it was the pump so I changed it but it didn;t make an difference. The two things I'm wondering about now are either th thermostat in the boiler or the motorised valve are faulty. A friend o mine doesn't think it will be the valve because there is obviously som power getting to it. When the power is switched on the manual overid lever is quite loose and only seems to have any resistance at the las couple of millimetres. When the power is switched off the lever move to about halfway and has resistance all the way when I push it. I'v no sure whether I should change just the motor or the whole valve to see i it works.

Any suggestions would be appreciated.

Cheers,

Jo

-- YellowPlanet

[Christian McArdle]

First, check that voltage is getting to the boiler input. If not, then you have a problem outside the boiler. If so, the problem is inside the boiler. If you don't know how to safely test for voltage, then call an engineer. If you think it involves using neon screwdrivers, then DEFINTELY call an engineer.

If power has got to the boiler, likely culprits are wiring/PCB problems and, the most likely IMO, a broken gas valve or boiler thermostat.

Christian.

[Set Square]

You have a Y-Plan system [See

and scroll down to Y-Plan]

You should also have a thermostat on the hot water cylinder - which you didn't mention.

A few questions:

• Has it previously worked ok, and suddenly stopped - or has it never worked?

• What happens if you select Hot Water but not Heating on the programmer - does the boiler fire up then?

If the boiler works for HW for not for CH, it is either a wiring problem or a problem with the 3-port mid-position valve (most likely with the electrical acuator part of this).

If HW doesn't work either, it sounds like a boiler problem. As Christain says, check whether the boiler is getting a demand signal on its Switched Live input.

A few more things to check:

• Switch off all power to the system (at the FCU, not the programmer). The

3-port valve should return all the way to the HW position - and you should feel immediate resistance on the manual lever. Does it do this?

• Remove the actuator from the valve and check that the shaft of the valve isn't seized. [The 2 parts are separate, so no water will leak out when you undo the screws holding the actuator on]. The shaft should move fairly smoothly through 90 degrees from the HW to CH position - either by gripping it with a finger and thumb or, at most, using light pressure with a pair of pliers.

Let us know what you discover, and we'll help you to home in on the problem.

[Sometimes, when the actuator gets 'confused', the simple act of removing all power and then turning it on again will get it going - a bit like re-booting your computer!]