Potterton Netaheat 10-16 not working

[Pants]

I have a Potterton Netaheat 10-16, the boiler fires up for a short while then cuts out and will not come back on until the outer cover is removed and replaced.
When I turn up the boiler thermostat it clicks but nothin happens (the relay doesnt energise) there is a closed cct across the pressure switch but open cct across the mercury vapour valve - so I believe the latter is at fault, any ideas and what is its purpose?

 

[ChrisR]

Netaheats are usually mendable but they're dangerous old things. Please leave it to a boiler engineer who understands this model. Not one to diy with.

 

[Trance Nation]

I have a Potterton Netaheat 10-16, the boiler fires up for a short while then cuts out and will not come back on until the outer cover is removed and replaced.

Be very careful with that potential death trap.

Get a Corgi in to work on it as advised above.

 

[Agile]

Being a positive pressure combustion chamber boiler this model can potentially kill with CO if the case has not been correctly refitted and tested to ensure there is no leakage.

This is a prime example of how a DIYer could create a dangerous situation from a lack of understanding of the design.

Tony

 

[Mike4]

I have a Potterton Netaheat 10-16, the boiler fires up for a short while then cuts out and will not come back on until the outer cover is removed and replaced.
When I turn up the boiler thermostat it clicks but nothin happens (the relay doesnt energise) there is a closed cct across the pressure switch but open cct across the mercury vapour valve - so I believe the latter is at fault, any ideas and what is its purpose?

I'll second what Tony just said. The case MUST be correctly fitted for this boiler to be safe.

Anyway, as yours has a relay, it must be one of the earliest models. As removing then replacing the case seems to make the difference, it may turn out that the physical disturbance is affecting a loose connection.

Turning up the thermostat energises the relay directly by making the neutral connection IIRC. (Live is connected via the mercury vapour switch). You could have a dead relay (Maplins) or you could have a dead MVS (dead boiler, as they are no longer available). You don't need to take the case off to test either component. The MVS should be closed circuit when cold, so that looks like the culprit. The MVS detects the presence of the pilot light, and allows gas to be delivered to the main burner when its phial warms up.

Cheers,
Mike4

 

[Agile]

It might even be that the case IS leaking and defeating the air flow test !

Tony

 

[ChrisR]

Won't be that one - these bloody things run quite happily with the boiler case missing!!
So they don't even test their poxy dangerous pressurised case.



They don't make 'em like they used to.

Thank god.

 

[ollski]

Won't be that one - these b****y things run quite happily with the boiler case missing!!
So they don't even test their poxy dangerous pressurised case.



They don't make 'em like they used to.

Thank god.

Exactly the thing that makes them such a killer when the backplate has rotted through.

 

[Pants]

Thanks guys for your rapid response,
Dont think I will mess to much with this boiler! Will get corgi to have a look, although I have already tested and eliminated the fan and the relay are both in good working order but the MVS is open cct when cold - must be the culprit. I have seen these on various websites:
http://www.boilerpart.gbr.cc/3034/prod.asp?p=102
http://www.onlineboilerspares.co.uk...2b4a7bcbb5d5ec6cc08c254635a97aaf&cPath=69_270
but not sure of their availability,
Is it worth repairing? I believe its been in the house since 1976 - never had any problems with it till the rad water pump packed up the other day, so got a new one fitted but seems to have upset the boiler

 

[Agile]

It is seriously overdue for replacement on efficiency grounds.

The mercury switch is normally open and closes on heating up by the pilot light to bring on the main burner. There is a resistor in series with the main burner solenoid.

Chris's takes about 40 secs to respond to the pilot and bring on the main burner.


Tony

 

[Pants]

So perhaps the MV is ok, from cold the switch is open. Maybe the thermostat needs replacing, boiler is totally dead at present, the termostat clicks but there's absolutely nothin else, no relay clicking or fan either? Might take a trip to the Potterton Graveyard

 

[Mike4]

The mercury switch is normally open and closes on heating up by the pilot light to bring on the main burner.

Tony

Hmmm.... interesting.

I spent several hours reverse-engineering the ignition sequence on this boiler a couple of years ago, and these are the notes I made. I established the MVS microswitch was closed in the cold/relaxed state.


Relaxed state:

When the boiler is off, the (relay) solenoid is relaxed. Live power is permanently fed to the fan, but it does not run because switching is in the neutral connection. (Live power is also fed to the pump overrun timer inside the boiler thermostat box, but no live power is fed to any other part of the boiler.)

Neutral goes permanently to the boiler thermostat inlet (terminal 3). When the boiler is cold the boiler thermostat will be calling for heat, and neutral from the boiler thermostat outlet (terminal 6) goes to terminal 2 on the relay (energising coil).

The outlet of a ballast resistor is also connected to terminal 2 (energising coil)(neutral switched by the boiler stat) of the relay. Don’t know what the ballast resistor is for.

The fan neutral lead connects to the inlet terminal of switch 1 (of two switches) (pin 1) in the relay. The neutrals of the solenoid, the spark generator and the fan are all in parralel, and switched by the switch inside the relay. The switch is open when the relay is relaxed, so the fan, sparker and solenoid do not operate.

Operation:

When a call for heat signal arrives, live goes to the 1A fuse. The fuse feeds live power to the inlet terminal of switch 2 in the relay (pin 7) and the inlet terminal on the APS microswitch. (Live power goes no further through switch 2 in the relay as it is open when the relay is relaxed.)

Live power passes out from the APS from the NC terminal. It goes to the inlet of the ballast resistor and the inlet of the mercury vapour switch (MVS).

Live power passes through the MVS when it is cold, and out along lead 20 to the twin spade connector on the Paxolin board. Lead 14 then takes the live power to the inlet of the relay coil (terminal 7). When the boiler thermostat is calling for heat, the neutral connection to the other side of the relay coil will be made, and the relay will energise.

When the relay energises, switch 1 in the relay closes. The relay will remain self-energised via its own switch 2 (terminals 2 and 6, with 6 connected to 7, the energising coil inlet). Switch 1 (terminal 3) is permanently connected to neutral, so neutral power is connected to the fan, sparker and solenoid gas valve, and the ignition sequence begins with the fan starting. The sparker and solenoid do not start yet because they get their live power from the NC connection on the APS.

Once the fan is running the APS operates and switches power from the mercury vapour switch to the sparker and solenoid.

Once the pilot lights and warms up the MVS, the MVS (mechanically) opens the gasway to the main burner and the boiler lights.

When the boiler reaches temperature, the boiler stat disconnects neutral from the relay and de-energises the fan. The APS relaxes and de-energises the solenoid and the boiler shuts down.


Have I got it wrong Tony?

Cheers,
Mike4

 

[libby lou lou]

I think sometimes we should listen to advice when given by other people.

Especially when it comes to Safety

I will have a go at most, if not all things, anything, even my boiler, but, when told to leave it alone,by these good people, who are the best at their job, and that's why your here, asking the questions.

I personally believe it's a death trap,get rid, is your life not worth a grand or two to put things right,

 

[Pants]

I believe it to be a Netaheat 10-16 mk1 ser. no. 22892 and been looking on this web site at schematic drgs, but none seem to match exactly?

http://www.partsarena.com/baxi/

But warnings heeded, just thought it might be somethin simple like changing APS, thermostat or Spark generator myself & saving a few quid but curiousity aint gonna kill this cat, will be on the phone tomorrow.

Very grateful for all the advice
Graham

 

[ChrisR]

But they are Ok, if checked and in good condition. I do Landlord's "Certificates" on a few every month.
Mine is (as I grasp the beech desk) ok for the time being. I have no problem getting spares, indeed there'a MVS new in its packet on that same desk.

Your memory is slipping Tony, that clunk took more like a minute when I timed it for you. Can't say I've bothered since!