Intermittent Hot Water Problem

[shearsy]

Hello everyone,
i went to an Alpha C27 on Friday after being told that it had no hot water. It was working fine so left it that I would replace the flow switch if it continued to cause problems.
The householder explained that it had happened twice in the morning over the last couple of weeks, once with the first shower of the day and once with second, it had also done it whilst using the kitchen tap. I had a call this morning to say its happened again. I'll be going back to replace the flow switch asap. Question is can a different fault cause the flow switch to act up? i.e extremely cold water or low flow rate through the system. I tested the switch electrically and it seemed to have an erratic reading whilst not in operation which then calmed down to almost zero whilst in operation.

 

[gasmarc]

when you say an erratic reading what do you mean ohms or continuity ?

 

[shearsy]

I tested the voltage across the terminals and to earth, was that correct?
Because its not a thermistor resistance isn't really applicable is it?
The reading fluctuated around the 24v mark, it didn't seem to settle down at all. When the boiler was in operation it went down to almost zero.

 

[gasmarc]

interesting what are you measuring exactly ?

 

[shearsy]

I was trying to see if the switch was working by measuring the voltage difference across the terminals. I thought that when the tap wasn't running there would be a difference and once the switch made there wouldn't be. If it was broken then there might have been voltage on one side but not the other and there would be no change when a tap was run.
It's kind of immaterial as it was working whilst I was there. I'd really like to know if there is anything which would cause an intermittent fault on a flow switch apart from a faulty flow switch. Could the PCB interfere or would a thermistor cause the hot to work intermittently?
I'll be going back to replace the switch and was asking because I didn't want to change it and for the problem to still be there with a new switch in place.

 

[gasmarc]

i have had this issue before on a ravenheat I went and bought the new flow switch for £60 and arrived on job only for it to be working correctly ,i am sure someone will put you right who knows alphas ,good luck