Glow worm Fuelsaver 25-30: intermittent operation problems

[staithes14]

We have a rather elderly boiler, a Glow worm 25-30, which has worked fine until just these past few days. It heats up a cylinder on the floor above.

On Friday however, it failed to come on for the evening shift. The pilot was lit, timer set properly, and the thermostats were all set right.

Nothing I could do could persuade it to come on, then, mid-evening, it clicked on and worked fine, some 3 hours late! Since then, it has repeated a variation on this every day. The timer light comes on, nothing happens, then at some point, the boiler kicks in (or not) at a random time.

I'm convinced the boiler is working fine, ie. it isn't a plumbing problem. The pump is newish (18 months old) and works fine when the boiler kicks in. It seems to be an electrical fault. A couple of times, I've seemingly got it to work by turning the cylinder stat up to 70 or 80, but I have no idea how that works.

Has anyone come across similar problems? If it is just a stat or a thermocouple or some such, it's something I can do, or have done, cheaply and easily, so all advice welcome. We're a bit skint right now, so can't afford a plumber, and it's bloody freezing!

Ironically, my brother's a CH engineer (ex British Gas) but he lives in Galway, so not much use to me.

 

[gas4you]

If you have a fully pumped system it could be a sticking zone valve, or microswitch in the head.

It could be ths gas valve is ticking. When it doesn't work as instructed you need to check for 240V at the gas valve terminals (if you are comfortable with testing live electrics).

If voltage is there it confirms gas valve sticking.

 

[staithes14]

Gas valve? That doesn't sound like a DIY job...

 

[gas4you]

No, it's not, if it is that. RGI needed to check it out properly.

 

[staithes14]

Well, the heating should be on (indicator light on clock is lit up). Just checked for voltage and there's none. Poked a neon tester into the live input terminal and nothing.

 

[gas4you]

I believe this model has a pcb in it, try gently tapping the relays.

If not you will have to trace back logically, to find the point where the 240V has stopped.

 

[staithes14]

Hmmm...no sign of a pcb anywhere. The electrical side is very simple indeed - input terminals, then a transformer, then a thermostat. Nothing else except a basic thermocouple leading up to the boiler.

I've no idea of its age, but it's to BS 800: 1977!

 

[gas4you]

All I can suggest is tracing the path of 240V to the point it stops then.

If it is present at the boiler live or S/L then it's a problem with boiler, if not then a problem with the controls outside of the boiler.

Don't assume the programmer is working just because the red light comes on.

 

[Agile]

You should check for power in and out of the boiler thermostat!

Unfortunately, even the simplest fault finding on a basic boiler like yours needs a multimeter and the skills to use it.

"Plumbers" who work on boilers are not all that ignorant as they require considerable skills if they are able to repair boilers. Thats apart from the training and assessments to pass the gas exams every five years to continue their CORGI registration.

Are you sure you cannot afford a plumber? Most people I come accross will pay anything to keep warm!

Tony

 

[staithes14]

OK, I've established that when the hot water demand kicks in, the boiler comes on and works fine, as it should. It's only the heating demand that fails to produce a response from the boiler. So it ain't the boiler.

Sigh...

 

[gas4you]

Next check any 3 port of ch zone valve. If you have 2 zone valves identify the ch one and check for 240V on the orange wire when it is open and demand is for heating.

 

[staithes14]

Are you sure you cannot afford a plumber? Most people I come accross will pay anything to keep warm!

Tony

Not right now. Don't want to go into details but unlike most people we can't just whip out a credit card or stick £100 on the overdraft.

As the boiler responds to demand for HW, and the pump etc are working, it 'must' be something like the clock's CH circuit.

 

[staithes14]

Next check any 3 port of ch zone valve. If you have 2 zone valves identify the ch one and check for 240V on the orange wire when it is open and demand is for heating.

Is that the 'A-B' valve (in a small metal box) near the CH pump? Has a little lever poking out of one end?

 

[gas4you]

Yes, if it has 2 pipes it is the ch one you need to check, if it has three pipes then I suspect that the actuator head microswitch has broken.

If it is the 3 port, do your radiators get hot when set for heating & hot water?

 

[staithes14]

Yes it's a 3-way valve. inlet port and A-B outlets.

I've put the hot water and heating to 'on' and yes, the rads are now heating up.