Boiler locks out and won't restart until cool - Help Please!

[skidderowe]

My system .....

Glow Worm Micron 50FF Boiler
Honeywell Programmable Timer (Heating & Hot Water programmed independently)
Honeywell Room Stat
Grundfos UPS 15-50 Water Pump
3-Way Motorised Valve


Here's my problem.....

When called upon by either heating / hot water or a combination of both, the boiler fires up and runs for approx 2 minutes. It then turns off and will not start again. If I leave it to cool down and then reset it, it will start but the same thing happens again.

My first thoughts were a faulty boiler and I have replaced both the thermistor and the PCB (both known problems with this make of boiler) but this hasn't made any difference. The boiler is 4 years old but the rest of the system is the original (about 25 years old).

I have also loosened the plug on the water pump and made sure that the pump is free and not seized up but I don't know if the motor is working or if the 3-way motorised valve is functioning correctly. Does anyone know how I can make sure these are working correctly? Would a problem with either the pump or the 3-way motorised valve cause the problem that I have?

Any help or suggestions much appreciated!

 

[gas4you]

Check for 240V AC at the pump terminals, the pcb supply's the pump voltage.

If it is there, can you feel the vibration of the pump spinning, or hear it with a screwdriver against it and the other end to your ear?

 

[EliteHeat]

Check for 240V AC at the pump terminals, the pcb supply's the pump voltage.

If it is there, can you feel the vibration of the pump spinning, or hear it with a screwdriver against it and the other end to your ear?

Or, after checking that it has 240V, just change the thing 'cos it definitely is not working.

 

[showerhead08]

Hi there

I am guessing your pump is actually inside the boiler?

Does your boiler have a fan?

 

[skidderowe]

Hi there

I am guessing your pump is actually inside the boiler?

No, the pump is seperate to the boiler and is in the airing cupboard next to the water cylinder.

Does your boiler have a fan?

Yes and it is working ok

 

[Gasguru]

When the boiler cuts out feel the flow pipe from the boiler....is it roasting hot? If so perhaps there is a lack of circulation. Have you removed the center screw/cap on the pump and checked the pump shaft turns with power applied?

 

[showerhead08]

if the pump is separate from the boiler then the pcb doesn't control the power to it.

the fan works, are the fan pressure hoses OK?

 

[gas4you]

Yes it does. The Micron is the same as the Solo3, pump is wired to the boiler terminals (pcb) so the boiler controls the pump over run.

 

[twgas]

if the pump is separate from the boiler then the pcb doesn't control the power to it.

the fan works, are the fan pressure hoses OK?

have you ever worked on central heating before? I dont think your comments will help anyone!!!!!!

 

[showerhead08]

yes i have worked on CH before and yes I may be able to help.

It depends if the installer used pump overun.

Sometimes if the fan isn't working to the correct speed then the boiler firing sequence will not work/cut out. The air pressure switch may prevent this.

 

[skidderowe]

When the boiler cuts out feel the flow pipe from the boiler....is it roasting hot? If so perhaps there is a lack of circulation. Have you removed the center screw/cap on the pump and checked the pump shaft turns with power applied?

Yes, have now identified lack of circulation as the problem and this seems to be caused by a dodgy pump.

With the power on, I removed the screw on the pump and manually turned the shaft. It was free to rotate and at first nothing happened but I kept turning it and then if fired into life and everything worked! It has packed up a couple of times since, but if I do the same thing again it works so I will get a new pump fitted, which hopefully will resolve the issue.


Thanks Gasguru and to everyone else for your help

 

[poolebybirth]

WTF!!!! the pumps rotor shaft turns and nothing and then all of a sudden it kicks in!!! that is nonsense, either the pump turns or not, turning a pump rotor shaft through the centre screw will not all of a sudden give it magic power! a very dodgy post this is....

 

[nickso]

WTF!!!! the pumps rotor shaft turns and nothing and then all of a sudden it kicks in!!! that is nonsense, either the pump turns or not, turning a pump rotor shaft through the centre screw will not all of a sudden give it magic power! a very dodgy post this is....

its sticking you moron.

 

[poolebybirth]

if it's sticking then it wouldn't be turning freely like the OP said would it!

 

[nickso]

if it's sticking then it wouldn't be turning freely like the OP said would it!

no it was free to start turning with a screwdriver, it wasnt free enough for the motor to turn it obviously.

who are you anyway? are you taking the **** with your posts as they are really strange