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Rick Ridley
Rick Ridley, UK Heating Engineer
Category: UK Plumbing
Satisfied Customers: 1561
Experience:  30 Years on the tools, now retired, Ex CORGI
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Rick, I have a problem with dhw on my boiler. Hot only when

Customer Question

Hi Rick, I have a problem with dhw on my boiler. Hot only when heating on. I changed the diaphragm on the diverted as it was perished. Diverter is operating the micro switch which appears to be doing its job. I'm getting about 4 volts through it? Boiler still will not fire up when I demand hot water. Temperature thermistor reads about 13000 ohms cold. Any idea what could be wrong? Glass fuses on pcb are okay.
Submitted: 1 year ago.
Category: UK Plumbing
Expert:  Andrew Smith replied 1 year ago.
Does the boiler not fire when you you turn on the hot tap?With the boiler off can you hear it click when you run the hot tap?
Customer: replied 1 year ago.
Yes the micro switch is operating. I am getting about 4 volts through it. I tested the thermistor also. It gives me around 13000 ohms.
Expert:  Andrew Smith replied 1 year ago.
4V? Both sides?What happens if you turn the power off and test continuity through it?
Customer: replied 1 year ago.
4v one side when no demand and then 4v the other side when switch activates. I took the micro switch off. There is continuity through it and when I activate the switch continuity moves through to the other connection. I thought this was working normally but don't know what the voltage should be.
Expert:  Andrew Smith replied 1 year ago.
You should be getting at least 12v through it, can you follow it backwards to see if it is a poor connection?
Customer: replied 1 year ago.
Ah got you now. Sorry Andrew. You meant input and output of micro switch. Yeah I have only 4v at the constant live. I'll try trace it back, see where/if I get 12. If not the connections is it likely the pcb?
Customer: replied 1 year ago.
Hi Andrew, I must have had a bad earth before! I'm getting more voltage through micro switch now. Readings as below.
No demand
C: 10v, NO: 26v & NC: 10v
On demand
C: 22v, NO: 22v & NC: 10v
Is this normal? Any ideas now?
Expert:  Andrew Smith replied 1 year ago.
Thats better -around 24v and it should be working, but if it is not firing then it is a suspect relay on the PCB.You may have to buy a new PCB to cure this
Customer: replied 1 year ago.
Oh no! That's what I didn't want to hear. Would you change the pcb now if you were on a call out? Would you try change the relay if it was your boiler? Where would this relay be in the circuit. There is a diagram on the cover of the electrical box. I'm a meccy fitter to trade sparks on hand.
Expert:  Andrew Smith replied 1 year ago.
Try and get a recon one online first