Potterton netaheat electronic problem

[jbadd]

My Potterton Netaheat 6/10E (CG No. 4160168) has for a few months now suffered from an intermittent fault that is becoming increasingly more frequent. I have followed the operational flow chart in the manual and the fan switches on ok, the ignition sparks ok, the pilot light lights ok, and usually the main burner fires ok, but sometimes accompanied by what sounds like a very noisy sticking oscillating valve the main burner goes out (but not always). Often coming on seconds later with more noisy valve sounds. A thump to the base of the boiler casing often works. I've checked the voltage to the solenoid valves: terminals T1 to T3 GV1 main burner is 240 vac which is correct; terminals T2 to T3 GV2 pilot is 172 vac (should be 240 vac). But I don't have problems with the pilot only the main burner which looks like it's getting the correct volts. Does this mean I've got two problems gas valve and the electronics board and the fans getting noisy too. All these parts could add up to £300 to £400 plus vat plus fitting. The boilers ~ 20 years old and hasn't had any new parts in at least 10 years. I would seriously think about a new boiler and according to the 'guide to the condensing boiler installation assessment procedure for dwellings' this will have to be a condensing one, but there do seem to be many restrictions on condensing flue positions e.g. 2.5 m from boundary, not over footpath or patio, not visible from front of building etc. are these all compulsory? If so it means I will have to re-site a new boiler which will not only be expensive but very disruptive re-routing gas and water pipes, and ending up with the boiler in a non-ideal position. To avoid this I would like to get my current boiler working correctly.

 

[ChrisR]

SOrry I don't recognise the fault (but I'll have more spares when I take my Netaheat out this summer!). Could be the pcb beginning to pack up.
New condenser shouldn't be too bad, many have plume diverting kits now which you can use to take it up the building, etc.

I serviced one of these recently which was a nightmare. Everything fell apart including the asbestos panels!

That 172 voltage sounds odd - anyone?

 

[bathjobby]

My Potterton Netaheat 6/10E (CG No. 4160168) has for a few months now suffered from an intermittent fault that is becoming increasingly more frequent. I have followed the operational flow chart in the manual and the fan switches on ok, the ignition sparks ok, the pilot light lights ok, and usually the main burner fires ok, but sometimes accompanied by what sounds like a very noisy sticking oscillating valve the main burner goes out (but not always). Often coming on seconds later with more noisy valve sounds. A thump to the base of the boiler casing often works.

I had exactly the same symptoms as this on my Potterton (different model) a year back and traced the fault back to a dry joint on the output leg of the transistor which switched the main gas valve open. At the time there were several other posts and threads around stating many instances of dry joints on Potty PCBs. I know this doesn't match with your voltage observations but thought it may help ! 172 volts may be around the effective voltage for the valve, hence the oscillating. Are you sure that isn't the main valve ?

 

[croydoncorgi]

Phrases like 'New Wine, Old Bottles' and 'Throwing Good Money after Bad' come to mind.
A boiler of that age is unlikely to pay you back after further investment in new parts.
And the Netaheat is not very efficient, in these times of rising gas prices...

 

[bathjobby]

And the Netaheat is not very efficient, in these times of rising gas prices...

Define efficiency ! The first thing a new appliance has to do is repay you its outlay; £2k, £2.5k plus ?
How long is the 10% or even 17% or so efficiency (if you believe it) of the new boiler is it going to take to recoupe £2.5K ? Anwers is NEVER.
If it aint broke (or in this case if you can fix it) don't change it....

 

[Soggy_weetabix]

replace eathing bracket and ignition lead.

Or adjust bracket to allow rectification. (both need a CORGI man as case seal will be broken to allow change)

Failing that a PCB change may be needed.

GOOD BOILER! Keep it

David

 

[Soggy_weetabix]

in addition to above, main burner solenoid can be replaced, but only if your fortunate enough to have a CORGI man who has an old white rodgers vlv to take apart.

E/Bracket change is a £50 job in south beds

PCB £150

Gas vlv the same as pcb.

All very easy for a gas engineer. (all prices include parts)

Upgrade your system, not your boiler.

David.

 

[geoff@cetltd]

SOrry I don't recognise the fault (but I'll have more spares when I take my Netaheat out this summer!). Could be the pcb beginning to pack up.
New condenser shouldn't be too bad, many have plume diverting kits now which you can use to take it up the building, etc.

I serviced one of these recently which was a nightmare. Everything fell apart including the asbestos panels!

That 172 voltage sounds odd - anyone?

If you look on the netaheat pcb, you'll see a green powewr resistor just behind the grey connector (5kohms). Once flame sensing has occurred, there is a relay on board which switches the supply to the pilot valve via this resistor

And yes, Netaheats do suffer from cracking solder joints, but in this case, the iscillations at the gas valve are more indicative of a capacitor on the pcb on it's way out

 

[geoff@cetltd]

in addition to above, main burner solenoid can be replaced, but only if your fortunate enough to have a CORGI man who has an old white rodgers vlv to take apart.

E/Bracket change is a £50 job in south beds

PCB £150

Gas vlv the same as pcb.

All very easy for a gas engineer. (all prices include parts)

Upgrade your system, not your boiler.

David.

I thought that the pcb was £120 (if you insist on buying a new one, that is

pcb replacement is a simple DIY job

 

[Agile]

Sometimes the solenoid coil has dirty connections to the connection block between the two coils.

Also there is a resistor built into the base of the mercury vapour switch which from memory is in series with the second solenoid.

Both those are possible failure points if the more common ones are not the problem.

Tony Glazier

 

[geoff@cetltd]

but that won't explain the "oscillating gas valve"

This will only buzz because of how its being driven, and this comes down to a capacitor on the pcb

 

[jbadd]

Thanks for all the responses, a good proportion of the respondents suggested PCB problems, so since this was an area that I could look at, I had another go. Found that measuring the voltage across T1 and T3 (main gas valve G2) got 240 vac which is correct but when valve oscillated this jumped about a bit, difficult to see over what range with slow response LCD meter. But more interestingly increasing and reducing the probe pressure on T1 terminal caused oscillations to start and stop, tried this a few times to make sure it wasn’t a coincident. Terminal connections looked good, so thought it may be the pressure was slightly flexing the pcb and opening up and closing a track break. Removed PCB, which all looked in remarkably good condition, no blackened components, no loose connections, no obvious dry joints no broken track under a x6 magnifier. Resoldered all terminal joints and a few others that looked less good than the rest, but no great conviction that it would help. Tweaked component wires to check for bad contact but all OK. While removing pcb earth lead spade connector to boiler earthing bolt noticed that this bolt was loose (a bit worrying as this looks like the boilers main protective earth connection). But the earth lead to the pcb this can’t be a protective earth since the pcb has no exposed metal parts, is it part of the spark ignition trigger return circuit and does it have any other circuit function that could account for my boilers symptoms?

Anyway the bottom line is that when I put it all back it now works well and has done so for the last 24 hrs. – long may it last! I still have 172 vac on the pilot valve drive, but that seems to be sufficient (manual says 240 vac correct).
But I still don’t know why it didn’t work and now it does, I find it hard to believe that what I did actually fixed anything.

 

[geoff@cetltd]

Aah, but you did

Flame sensing is referenced to earth, so an unreliable earth means unreliable flame sensing which means intermittent main valve operation