Cylinder stat

[noddy997]

Folks my seasonal problem has improved since I installed soffit vents to 2 sides of the property.

However, twice in one week when HW goes off at set time on programmer the heating goes off too. When you try putting HW or CH back on nothing happens.

If you leave it on, the pump eventually kicks in and stays on for several minutes but the boiler doesn't fire up. As before no fault codes on boiler.

The problem would be more regular without the soffit vents and during March to end of Sept both HW and CH function normal without issues.

Due to fit a PIV system so any bad air could be pushed out of the loft xD

I am trying to test certain wires for readings but by the time I get tools out boiler kicks in.

Wiring plan

1) Room stat to white
2) Boiler to pump live
3) HW on to Cylinder stat common
4) Earths
5) HW off, Grey, Cylinder stat satisfied
6) Neutrals
7) Yellow to boiler switch live, Orange, Cylinder stat call for heat
(all other wiring is downstairs by the boiler)

This video suggests a faulty cylinder stat could be the issue.

 

[Stuckinarut]

Could be the cylinder thermostat, are you going to test for voltage like in the video too?

 

[Harry Bloomfield]

I am trying to test certain wires for readings but by the time I get tools out boiler kicks in.

You could try installing some test lights. They needed be any more complex, than neon indicators, wired between the suspect connections and the neutral.

A while ago, I set up a row of LED's, as a quick way to monitor, my heating system - I never actually needed it, no fault ever developed. Just a cheap 5mm LED, a capacitor, and a diode, needed to have one work on mains voltage.

 

[noddy997]

Could be the cylinder thermostat, are you going to test for voltage like in the video too?

Possibly but my loft hatch is in the corner of the house, requires a ladder from the garage, by the time you set up and crawl to the centre of the loft it starts working again. It's a pain in the backside. Things would be quicker if there was a loft hatch ladder in the landing. Honestly why did they fit loft hatches in the corner of the house never makes sense....

 

[Johntheo5]

Folks my seasonal problem has improved since I installed soffit vents to 2 sides of the property.

However, twice in one week when HW goes off at set time on programmer the heating goes off too. When you try putting HW or CH back on nothing happens.

This video suggests a faulty cylinder stat could be the issue.

It could also be something in the programmer because you need both the HW ON contacts and the HW OFF + the CH ON contacts to enable anything to work, maybe the programmer is damp, have you tried drying it out with a hair dryer when the problems occur?.

 

[noddy997]

It could also be something in the programmer because you need both the HW ON contacts and the HW OFF + the CH ON contacts to enable anything to work, maybe the programmer is damp, have you tried drying it out with a hair dryer when the problems occur?.

But why would the pump kick in and the boiler doesn't when something is selected on programmer

 

[Johntheo5]

A good question if the boiler still doesn't fire after several minutes, I have a oil fired boiler which cycles and sometimes the boiler doesn't refire for a 10 minutes or more (after a recycle or a new demand from the programmer) after the pump restarts until the boiler flowtemp is ~ 10c below the target temp (hysteresis) but doubt if thats your problem especially if you have a gas fired boiler, is it a system or heat only heat only boiler?, a system boiler will tell the pump and burner to start when it gets a switched live signal from the programmer, the burner should refire when the boiler flowtemp is at targettemp-5C.

 

[Stuckinarut]

But why would the pump kick in and the boiler doesn't when something is selected on programmer

Not enough voltage being delivered to kick it in perhaps.

 

[Harry Bloomfield]

But why would the pump kick in and the boiler doesn't when something is selected on programmer

A fault at the actuator could possibly cause that.

 

[noddy997]

Not enough voltage being delivered to kick it in perhaps.

But doesn't the boiler tell the pump to fire?

So will that be a wiring issue?

 

[noddy997]

A good question if the boiler still doesn't fire after several minutes, I have a oil fired boiler which cycles and sometimes the boiler doesn't refire for a 10 minutes or more (after a recycle or a new demand from the programmer) after the pump restarts until the boiler flowtemp is ~ 10c below the target temp (hysteresis) but doubt if thats your problem especially if you have a gas fired boiler, is it a system or heat only heat only boiler?, a system boiler will tell the pump and burner to start when it gets a switched live signal from the programmer, the burner should refire when the boiler flowtemp is at targettemp-5C.

Heat only boiler. The problem is very intermittent

 

[Johntheo5]

The problem would appear to be the boiler itself if its getting a switched live from the programmer, the boiler will then use its own permanent live to start the pump and fire the boiler, pump is starting but boiler isn't firing.
Is the boiler in these sometimes damp surroundings as well?.

 

[Stuckinarut]

But doesn't the boiler tell the pump to fire?

No. Usually a motorised valve sends a switch live to the boiler and pump. You could have stray voltage, a wiring issue, a control fault to name a few. Probably best employing the services of a decent heating engineer or electrician who's competent in this area.

 

[Johntheo5]

My oil boiler works from the motorised valve but heat only gas boilers like the Vaillant 424 etc (heat only boilers) gets the signal to the boiler only, this then starts and manages the pump, pump overrun etc.

 

[noddy997]

The problem would appear to be the boiler itself if its getting a switched live from the programmer, the boiler will then use its own permanent live to start the pump and fire the boiler, pump is starting but boiler isn't firing.
Is the boiler in these sometimes damp surroundings as well?.

It is, humidity around 73% in the garage. However as you know with the vaillants the pcb is in a decent housing