Prima 50F - is this likely a PCB issue?

[dingo45]

The pump overrun has a Phial same as any other thermostat, and it will depend on the residual temp in the heat exchanger if it actually comes on or how long it stays on, and yes the water is circulated but the ABV then the overrun will control the pump, here isa pic of it

View attachment 284158

I managed to find that part new. Fitted today and now all working properly. Many thanks for the help.

 

[old duffer]

Boiler is firing its just the pump is not always running, nothing to do with the thermistors, which this boiler doesnt have anyway, it has a liquid control thermostat and it isnt that either

thermistor is the generic term for the measurement of electrical resistance in specific relation to temperature. The method used to do this is irrelevant.

 

[old duffer]

what did I say about it being a thermistor!
If you understand the very very basic operation of these heaters then diagnosing problems becomes very simple logic.
The idea that it must be complex and expensive is the stuff of plumber lol

 

[dingo45]

I'm curious, what happens in these overrun thermostats to result in poor contact to switched/permanent live? Is this metal fatigue in a bimetallic strip or something else?

 

[dingo45]

what did I say about it being a thermistor!
If you understand the very very basic operation of these heaters then diagnosing problems becomes very simple logic.
The idea that it must be complex and expensive is the stuff of plumber lol

With the benefit of hindsight and having got hold of the boiler installer manual, the overrun thermostat is unique in that it seems to be the only component that works independently of the pcb. The pcb seems to be the most prominent, therefore probably the most sought after, part for this boiler on ebay.

 

[ianmcd]

thermistor is the generic term for the measurement of electrical resistance in specific relation to temperature. The method used to do this is irrelevant.

Completely wrong, again this boiler does not have any thermistors

A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of thermal and resistor.

Thermistors are divided based on their conduction model. Negative Temperature Coefficient (NTC) thermistors have less resistance at higher temperatures, while Positive Temperature Coefficient (PTC) thermistors have more resistance at higher temperatures.[1] Hence, a PTC thermistor's resistance is directly proportional to temperature.

 

[ianmcd]

I'm curious, what happens in these overrun thermostats to result in poor contact to switched/permanent live? Is this metal fatigue in a bimetallic strip or something else?

As these thermostats switch over every time your heating is switched, the contacts tend to become charred with the constant making and breaking of the contacts, same as any other relay, hence sometimes they make sometimes they dont

 

[old duffer]

With the benefit of hindsight and having got hold of the boiler installer manual, the overrun thermostat is unique in that it seems to be the only component that works independently of the pcb. The pcb seems to be the most prominent, therefore probably the most sought after, part for this boiler on ebay.

What was your logical conclusion that came to the fact that something as important as an on-off switch such as a thermostat (its what it does) is not connected to the board?
You are way past your comfort point now, time to get someone who understands logic i.e. RISC chips and interconnects on logic boards (which BTW used to be what they were called on these simple boilers...becuase they really are simple logic)

 

[old duffer]

Completely wrong, again this boiler does not have any thermistors

A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of thermal and resistor.

Thermistors are divided based on their conduction model. Negative Temperature Coefficient (NTC) thermistors have less resistance at higher temperatures, while Positive Temperature Coefficient (PTC) thermistors have more resistance at higher temperatures.[1] Hence, a PTC thermistor's resistance is directly proportional to temperature.

OK, so you read a wiki...tell me how the term "directly proportional to temperature" is a different description to "measurement of electrical resistance in specific relation to temperature"? I can't wait to hear this one lol

 

[jeff the gasman]

Completely wrong, again this boiler does not have any thermistors

A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of thermal and resistor.

Thermistors are divided based on their conduction model. Negative Temperature Coefficient (NTC) thermistors have less resistance at higher temperatures, while Positive Temperature Coefficient (PTC) thermistors have more resistance at higher temperatures.[1] Hence, a PTC thermistor's resistance is directly proportional to temperature.

Portmanteau! That’s a big word for a Matelot! X

 

[dingo45]

What was your logical conclusion that came to the fact that something as important as an on-off switch such as a thermostat (its what it does) is not connected to the board?

I arrived at that conclusion, with hindsight, and having subsequently got hold of the the functional diagram. I didn't base my decision to replace the component based on that but rather the advice received here and elsewhere. Also, I don't think I said I performed the fix myself.
The diagram (I attached post #16) suggested to me that the power to the overrun thermostat isn't via PCB but rather direct from either boiler's permanent or switched live, depending on the state of the thermostat. You might want to reread this thread!

 

[ianmcd]

Portmanteau! That’s a big word for a Matelot! X

I know what the feck does it mean ?

 

[ianmcd]

OK, so you read a wiki...tell me how the term "directly proportional to temperature" is a different description to "measurement of electrical resistance in specific relation to temperature"? I can't wait to hear this one lol

you really are a clown, this boiler has a liquid filled phial , NO ELECTRICAL RESISTANCE is measured anywhere that is a thermistor this is a thermostat , liquid filled you old duffer

 

[old duffer]

you really are a clown, this boiler has a liquid filled phial , NO ELECTRICAL RESISTANCE is measured anywhere that is a thermistor this is a thermostat , liquid filled you old duffer

a phial? like your covid jab came in? LOL

 

[old duffer]

So as this is now an old thread, the poster must have resolved the issue. What was it then?