gas valve modualation

[leinster]

hi.
ive re3cently passed my ccn cen1 so fairly new to the industry. just a question regarding modulation. have i got this right---

gas valve modualtes in this order of sequence ntc (working ok)transmits corrosponding voltages via pcb to gas galve to modulate to the required demand?

if no modualtion is taking place or poor performance what will be the affect on ch and dhw demand- overheating? poor temp performance?

i assume if you suspect modualtion is the problem you would first do all the basic gas pressure tests, check to see if the modureg is correctly set up to mini and maximum settings,resistence and supply voltages.then in then fault find ing prcocess you would begin to look at defective thermistors , pcb not transmitting correct dc volatage to modureg etc?

any help would be great. thanks

 

[Trouble666]

A thermistor is a resistor and varies the resistance due to heat.They can either be NTC (Negative Temp Co-efficient)-the resistance reduces as the temp goes up, or a PTC (Positive Temp Co-efficient)-the resistance increases as the temp goes up.The thermistor works with in conjunction with potentiometer (customer control).The potentiometer is a variable resistor set by the customer. As the boiler heats up the thermistor changes resistance this is registered by the PCB which in turn reduces the voltage to the Modureg which when the resistance is matched from the thermistor to the potentiometer the PCB will stop energising the Modureg.
Thermistor faults may cause no operation at all or no operation of that element (e.g. Heating or HW). What kind of fault is it?

I'm doing my ACS in May, so although this is the best of what I know, it is not definitive!

Hope it helps