Paul Barker or Alpha boiler guy

[undercover]

I was asked to look at an Alpha CD28. Plumber had been there and drained the system to move rad. When he filled up and tried to start the boiler he was met with both the LED's flashing intermittently.

Fault guide says this is low pressure and i told him to check pressure, filling loop etc. LED's still flasing alternativley. I took a quick look this morning. Put my meter on the low pressure switch and got continuity. Could the low pressure switch still be faulty even with continuity?? eg: crud on the switch itself... would you recommend changing the switch??

Any ideas as to what else would be preventing the boiler from firing up??

Nick

 

[Agile]

Without looking up the boiler circuit, are you sure the boiler requires continuity to indicate pressure?

Did you try disconnecting one terminal?

Tony

 

[Paul Barker]

It does require continuity, these sort of switches can show continuity on your meter but still not pass sufficient current to satisfy the pcb so bridge it out to prove it, if it fails, isolate boiler drain, take it out clean it's hole and the pipework to it, retry it, if that fails; new one.

 

[undercover]

Thanks for the reply Paul. I'll try what you suggested.

PSo you know best place to source spares for this boiler?

Nick

 

[megawatt]

Guys, perhaps we should refrain from talking about continuity and start talking about resistance in these cases as continuity to a spark suggests such an insignificant resistance as to be ignorable.

In other words, you cannot have continuity across a closed switch which then restricts current flow ... This is a high resistance switch which does not have continuity.

Not trying to be picky just attempting to make things clear for OP's.

MW

 

[Paul Barker]

You're right, big mistake to think that because a meter goes beep a part is in the clear.

I get my Alpha parts from Sales at Alpha. They are just moving warehouse though so not a good time.

 

[Agile]

I disagree!

As you say continuity implies a very low resistance. Most meters beep with a resistance up to 200 ohms but the display shows the test voltage across the leads.

To use the meter correctly the display has to be interpreted and not just assume that a beep means its OK.

Many people fixing boilers dont even know how to decide what resistance range to select. For them the continuity range is going to be closer to the ideal.

Tony

 

[megawatt]

Not sure what you're disagreeing with Tony

 

[Agile]

I think its correct to mention continuity because thats perceived as being a very low resistance, say under 1 ohm.

If you say resistance then people expect there will be a resistance value of many ohms.

Tony

 

[megawatt]

Tony: The point I was making referred to Paul's post ...

It does require continuity, these sort of switches can show continuity on your meter but still not pass sufficient current to satisfy the pcb

You cannot have continuity and such a high resistance so as to affect the current to the PCB ... The two are incongruous.
MW