Myson Apollo 50B Boiler - Problems?

[_Ben_]

Hi there.

I've got a Myson Apollo 50B balanced flue boiler which exhibits interesting behavior. It's a standard Y-plan system with (brand new) Drayton controls and a Honeywell cylinder stat.

When the programmer demands hot water the boiler starts and heats the water, however if I cancel the programmer such that hot water is switched off, the boiler goes through a cycle of stopping and running (approximately 20 second run time). This appears to last for about 20 minutes. The boiler stat is set to "2" and the central heating pump is set to full speed.

Sounds iffy to me. The boiler is wired with a permanent live (for the purposes of an overrun pump or something) and also switched live to the "ON". Is the boiler designed to do this?

The house and central heating systems in general are new to me.

Any help is gratefully received!

Ben.

 

[pannierstan]

3 way valve is knackered and yes they are supposed to be wired that way.

Stan

 

[_Ben_]

Hi Stan,

Thanks for your response. The three way valve was replaced last week - what makes you think its that which is wrong? Could it be the circuitry in it which is causing the boiler to keep firing up?

Cheers,

Ben.

 

[gas4you]

Check that the pump over run is actually working.

 

[Agile]

If the valve was replaced by a professional then call him back!

If you replaced it yourself then you will have to mope!

Tony

 

[_Ben_]

Does the pump overrun mean that the pump runs on after the boiler has finished? Presumably to keep the water flowing whilst the exchanger cools down?

>> If you replaced it yourself then you will have to mope!

Replaced the valve myself as the radiators were coming on with the hot water, now the hot water works perfectly independently of the radiators. Wires were a like for like replacement as I used the exact part number for valve replacement

Cheers,

Ben.

 

[gas4you]

Does the pump overrun mean that the pump runs on after the boiler has finished? Presumably to keep the water flowing whilst the exchanger cools down?

Yes. Probably done by heat via the boiler stat on an old model like this, but I do not know for certain.

 

[_Ben_]

Yes. Probably done by heat via the boiler stat on an old model like this, but I do not know for certain.

Ahh okay, will check. Probably ought to get it serviced by a professional.

Thanks for all your help.

 

[Agile]

A "Y" plan needs a changeover connection on the hot water stat and a HW off connection on the programmer.

Sometimes these are not wired correctly by the installer.

Tony

 

[namsag]

Pump over run on these is a silver disc about the size of a ten pence coin on the bottom right hand side of boiler ... And will keep pump running for twenty mins after demand but would not allow boiler to fire

 

[_Ben_]

Hmm, some more things to think about. I'll have a double check of the wiring and perhaps get a meter on the back of the programmer to determine what is happening when HW is demanded off.

Thanks, will report back.

Ben.

 

[pannierstan]

The Pump overrun will not cause the boiler to cycle on and off. The only reason for whats happening if the boiler is working OK on Hot water is the 3 way valve.
If the wiring is wrong or the valve is stuffed it will bounce in mid position giving you just the syptom you describe.
I suggest that you check the wiring you did and then check the operation of the valve. Make sure it winds fully over to heating only. Grey and white wires the wrong way can cause a similar condition........or is that grey and brown on a zone valve.....ah the mind is clouding over again. Time for sleep

Stan

 

[_Ben_]

Guys,

Well done! Was a wiring fault in the (all too crowded) wiring backplate. Turned out that the pump overrun circuitry was connected to the boiler ON. I have to say not guilty but rule here is to never assume the previous occupants wiring was correct .

All fixed with no damage *phew*.

Cheers,

Ben.