Boiler won't light for central heating.

[RobNNN]

I have a 20-odd-year-old Baxi Bermuda 401 Gas Central Heating system.

When I try to switch on the heating, nothing happens. No click, no thump, no woof from the boiler lighting up, no big flame in the boiler, no heat in the rads. I do get a light on the Honeywell ST699 controller. The room thermostat seems to be okay - but even when turned way up there is no response. I have now replaced it with no effect - still nothing.

The hot water is fine. When I switch on the HW, I get a light on the controller, a click from the system, a woof sound and a nice big set of flames in the boiler. The water is piping hot in no time.

I can divert water into the rads for heat, but this of course turns off when the hot water reaches the max temp.


Any ideas?

 

[Iddy]

It it's a y-plan you've got, most likely the 3 port valve. To fault find you really need a multimeter... Check for 240v on the white wire of the 3 port valve. If there is, does the valve 'motor over' to the heating position? If not, it's the synchron motor in the valve. If it does move to the heating positiion, it should switch 240v onto the orange wire to turn on boiler and pump, if not, the microswitch in the 3-port valve has gone and you need to replace the whole valve. - Hope that makes sense...

As a temporary measure, you could take the cylinder 'stat off the cylinder to keep the boiler running so your heating stays on. Watch out for your hot water getting too hot though! Turn down your boiler 'stat as a precaution.

 

[45yearsagasman]

View media item 37352That's what to look for in the motorised valve. If found to be open circuit then its simple to change. Work safe and isolate electrics.

 

[RobNNN]

Thanks for those replies.

I am now beginning to close in on the problem. By forcing the switch on the valve (Honeywell, silver box in the airing cupboard) to the right and keeping it held down I can can fire up the boilers with the CH switch and get heat into the rads.

Woo hoo.

If however I either release it, in which case it springs back to the middle, or push it up into the catch which is supposed to keep it to the right, the boiler switches off. I have to keep it down and to the right with tape and perhaps later a metal clip.

This is only a temporary fix of course, but I have established that either the valve motor is busted or it is not getting a signal from wherever.

I will do more research on this.

 

[Hugh Jaleak]

There is some comprehensive information about motorised valves on page 2 of the FAQ's. Well worth a read.

 

[dreadnoughtheating]

I suspect the 401 model you have is a bit more than twenty years old.

The motorised valve top cover may have a 'raised dimple' on it, if it does, the head can be safely removed and replaced (Q&B sell them - I think, on sundays) If it does not have the dimple it is as asaid, a whole valve replacement task, inc a drain-down & refill.

DH

 

[RobNNN]

I cannot hear anything from the motor on the valve when I try to switch on the CH. Incidentally the valve is called a Honeywell 8951. There is no mention of V4073 anywhere on the box. In the boiler instructions it is called a Honeywell V4600C 1029. It looks just like the Honeywell valve that is pictured in section 10 of the FAQ.

I found the dimple on the case, and removed the cover. There is nothing obviously wrong, no burned areas.

I think it is probably the motor. (Synchron)

 

[RobNNN]

I hope someone can give me more help.

I have now removed the valve head cover and removed the motor from its mounting, leaving it wired up. I can see the motor gear, but nothing I do can make it move. CH - nothing, HW - nothing, both - nothing. I can move the gear with my fingers, though it is stiff.

A multimeter showed no current through the white wire and only about half normal through the grey. As far as I can see the wires in the box near the valve are fine - no bad connections. I have no reason to think that the wires are bad anywhere, but...

...could it be the programmer? I did get a new one (Honeywell ST699) which is outwardly identical to the old one. The wiring diagram inside the case is identical to the old one, however, the printed circuit looks different. The old and new programmers were made about 25 years apart, so I suppose that some things have changed. Anyway, they have identical effects, HW but no CH.

 

[Agile]

Did you measure the resistance of the motor?

Or apply 230v to it ?

Tony

 

[RobNNN]

Did you measure the resistance of the motor?

Or apply 230v to it ?

Tony

I don't have anything to test the resistance unfortunately.

I'll see if I can give it 230V.

Fingers crossed, but not wires hopefully.

 

[RobNNN]

I have now jammed the valve all the way over to the right side (further than the manual switch can take it) and I have CH wthout HW.

Survival is now guaranteed.

Now to find the problem - is it the motor or is it the wiring?

I need to know how to test the motor. Can anyone help?

 

[RobNNN]

I have replaced the motor and everything is fine so far.

Thanks for the help my friends.