Potterton Prima turning on and off

[West Country]

Hi everyone

I have an issue with my potterton prima boiler and would love some help. It works fine when either CH or HW are on but when they are off the boiler will fire up briefly and cut out again, it appears to be random and for 1\2 sec or severely seconds, it will continue doing this. I am turning off the power over night to stop it doing this.

My system is and old gravity-fed one, so I have HW or HW and CH. It had been working fine until last week, because the boiler seemed fine when CH or HW are on then I assumed (wrongly) that it was a control problem. Which is why I changed the old rotary dial switchmaster for a hive mini, but I still have the issue. This makes me think it's a problem with the boiler making it fire up without a signal from the controller.

 

[West Country]

I've attached a video so you can hear the noises.

 

[Ric2013]

I've attached a video so you can hear the noises.

Where?

 

[Deleted member 120897]

So you have an issue with noise and random firing? Noise could be lots of things, random firing sounds like motorised valve failure

 

[West Country]

Video so you can hear the noise

 

[West Country]

So you have an issue with noise and random firing? Noise could be lots of things, random firing sounds like motorised valve failure

So the motorised valve is for CH if I select HW only will this remove the input from the motorised valve and prove the fault?

Excuse my ignorance but I thought the motorised valve shut off the CH side of the system and didn't have an input to the boiler. I can hear when it closes and I certainly only remember hearing it operate when the heating is set to turn off.

 

[Deleted member 120897]

Video so you can hear the noise
View attachment 80397

Sounds like something is struggling like the pump or motorised valve.

 

[Deleted member 120897]

Might be best posting some photos of what you have valve wise and pump, etc.

 

[West Country]

So here you go. Top of boiler pipe work. I have a junction box, the controls (formally the switchmaster now hive) are wired into it. Live and neutral wired to the junction box via the controller Motorised valve to the junction box, junction box to the boiler. There is also a wire from the junction box going up stairs which a assume goes to the hot water tank. The pump is on the hot water and the motorised valve on the heating. I checked and I could hear the motorised valve close when I selected hot water without heating.View attachment 290356View attachment 290357View attachment 290358.

 

[West Country]

So here you go. Top of boiler pipe work. I have a junction box, the controls (formally the switchmaster now hive) are wired into it. Live and neutral wired to the junction box via the controller Motorised valve to the junction box, junction box to the boiler. There is also a wire from the junction box going up stairs which a assume goes to the hot water tank. The pump is on the hot water and the motorised valve on the heating. I checked and I could hear the motorised valve close when I selected hot water without heating.View attachment 290356View attachment 290357View attachment 290358.

 

[West Country]

Photos of how it's wired in case it helps

 

[West Country]

So some explanation may help:
Hive left cable permanent live and neutral, right cable HW on and CH on

Junction box:
Bottom left furthest left HW on and CH on, inner left permanent live and neutral.

Top left hot water tank

Top right mechanical valve

Bottom right go to the boiler.

 

[Ric2013]

So you have an issue with noise and random firing? Noise could be lots of things, random firing sounds like motorised valve failure

Funnily enough I had some very odd noises from my Potterton (Netaheat) "Profile" boiler starting Christmas morning lol. Sounded like a fan failure (fan sounding like it was fighting heavy wind, though sounded normal from outside), but turned out was the microswitch in one of my motorised valve intermittently making poor contact and only providing 200V to the boiler's switched live input (or that's how my analogue meter read it: possibly the connections were arcing and not a constant voltage at all?). Not the same as your noises, but who knows if the causes are related. If you don't have a multimeter, a low wattage lightbulb might do as a crude voltage tester - see if it goes flickery, that kind of thing.

There's something odd about the controls. Normally a gravity system (semi-gravity) uses the pump only for heating and relies on gravity for hot water only, hence why you can't have a water off, heating constant mode. Not saying this is the cause, but what I would want to know is what is providing the switched live to the boiler, as if there is a valve, the valve microswitch could be wired to switch the boiler on, rather than the boiler being switched direct from the Hive. I really can't see the boiler firing if the switched live isn't being fed, and, looking at a Prima manual, seems that it would be virtually impossible.

I'm not qualified, competent, or willing to discuss boiler faultfinding. However, from listening to your video, it sounded like the boiler was making fairly typical noises for a boiler of this type between the 2 and 4 second mark, and running the fan. Fans don't run without power, so I'm thinking an external control issue rather than a boiler one. If I'm correct, can we twin our boilers and both put little signs on them saying twinned with Potterton Prima / Netaheat Profile serial number xxxxxxxxx?

 

[West Country]

Hi everyone, so I've tried something for fault diagnostic purposes. I electrically disconnected the motorised valve and used the manual override. Still have the same fault, so I'm thinking (happy to be wrong) that with the valve disconnected and the controller replaced, it rules out external inputs and it means it's a boiler problem.

 

[Ric2013]

You disconnected all 4 cable cores (ignoring the earth, if present) on the valve? If so, I'm leaning towards your point of view.

Looking at your junction box, the boiler has two cables going to it. Is one the cable where the boiler feeds the pump? Only you have switched lives from the programmer to 5 and 3. I'm confused as to which of these goes direct to the boiler if the boiler isn't switched by a further external control.

Also, if your system is semi-gravity, the Prima manual I'm looking at (may not be your exact model) suggests it's suited to FULLY PUMPED systems ONLY so if it's installed differently (wrongly), then we need to assume the wiring will be unusual. Please define what you mean by 'gravity-fed' system. Do you mean it's 'open vented'?

As for the Switchmaster (an 800, perhaps?), may be worth flogging on ebay if it works!