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colinhat · 14 May 2006

Hi,
I'm hoping that someone will read this and instantly give me some advise. A couple of weeks ago my ariston combi boiler had a bit of trouble with hot water. The water it pumped out was luke warm and the boiler itself overheated after about 15 seconds and then restarted after it had cooled down a bit. The central heating worked fine. I'd come to the conclusion that a blocked diverter valve was backing up the hot water and causing the over heat. I'ld planned to look at this problem this weekend but Friday the whole system would'nt work. I've cleaned the diverter valve (full to bursting with radiator rust) which not seems to work fine. However there is still no flame with either hot water or central heating. I have not yet check for a blocked pump but no gas or ignition seem to be getting to the business end. Does one not work with out the other and would a block pump stop all of this. Sorry to go on, any help.

meldrew's_mate · 14 May 2006

Not much experience with these cheap and nasty Italian boilers, though if you've found your DV full of gunge it's pretty certain the main heat exchanger is too, and the pump. It maybe this model has a flowswitch on the primary circuit which is stopping the boiler from firing.

Suffice to say a full flush is required to remove as much of the gunge as possible. Follow this up by fitting a Fernox boiler buddy to the CH return to prevent the re-entry of more rust.

ChrisR · 14 May 2006

If the pump isn't pumping water a switch won't be closed which detects the flow in the boiler. So it wouldn't try to light.
You don't say which boiler it is, but look for one switch operated by the tap water flow, and another similar looking one, smaller diaphragm. May be on a separate casting or the same as the DV. Same idea, pin sticks out to operate switch when there's flow.
Guess that the pump is full of crud - undo the allen bolts and have a look inside, and at the impeller's gaps.
The heat exchangers will be in a bad way too, so as mm says...

Pretty average boilers, diverter is probably the same Giannoni as used on the much-praised Worcester Bosch cdi range!

colinhat · 15 May 2006

Thanks for the tips, have cleaned the pump and flushed the heat exchanger. The pump is working and I'm confident that the water is flowing freely. Still no Ignition. There is a "if boiler does not light press this button" but that also has no effect. gas is getting to the valve and all fuses are O.K. Any more ideas?

Gasguru · 15 May 2006

Tell us what model it is.

Some have pressure switches (that may be blocked)

Some have water flow diaphragm (that may also be blocked)

I hope you cleaned out the plate exchanger (if it has one)

Sometimes the pipework can be blocked on a fitting - a washer edge is sufficient to allow crud to build up and reduce flow.

Agile · 15 May 2006

The system flow switch is a key component, can you see a pin and switch towards the back left? Is the pin operating the switch?

Is there a red reset button in the middle of the overheat stat on the flow pipe on the left just below the combustion chamber which you will not be opening?

Tony

colinhat · 15 May 2006

The Model is an ariston euro combi 23(installed 2000). The flow switch is working and slids across when the hot tap is turned on. I can also press this switch manually and the boiler goes throu its start up (fan starts, pump starts, water flows) still no ignition. I've also just noticed that the heating pressure has risen. I'm guessing this is either due to a seepage from the DV or because I activated the switch manually. I only really found crud in the DV the rest was quite clean. Am I talking rubbish?

Gasguru · 15 May 2006

I guese you mean an A23MFFI Euroccombi.

The flow switch is working and slids across when the hot tap is turned on

This sounds like you mean the hot water flowswitch on the end of the diverter is operating OK.

You need to check the "main circuit flow switch", This is the switch on the front of the diverter (facing you).

Remove the switch and check the pin operates once the pump starts. Check there is sufficient force from the pin to activate the switch. Check the switch operates correctly by activating it with a small pin once the pump has started.

The pressure gauge will fluctuate markedly as the pump starts (normal)

If the pressure has risen without the pump on the fillling loop is letting by.

colinhat · 15 May 2006

Your assumptions are correct with the boiler. My Tech help guide that came with the boiler calls the switch at the front of the DV a "Group Circulator Consent Pressure Gauge" and consists of A wiring block, Black plastic housing, Spring, White plastic plunger and a rubber diaphram. I took that apart Sunday and cleaned it and put it back together again. Am I guessing that if I hold the housing in my hand and turn the boiler on it is supposed to zoom into orbit!! and how do I know there is enough power to activate the switch without filling the system. I think I'm starting to rule things out, which is good (or could be bad, really bad).

Gasguru · 15 May 2006

Sorry brain fade.

Yes the plastic circular bit contains a magnet and the switch is actually a reed switch.

Just short out the wires after the pump has started (they disconnect from the reed switch) - care they may be 240v

Check the small holes in the diverter are clear so the pressure can reach both sides of the diapgragm.

If you have re-newed this part (as the housing often leaks) have you fitted the correct spring (there are two supplied)

Sometimes even with a new assembly the reed switch is not soldered in the correct orientation and require modifing.

colinhat · 16 May 2006

Done as you have suggested, and if I unplug the wiring block from the main flow switch the fan goes out. when I short the switch the fan come back on again - does this mean that the switch is working? The 2 small holes in the DV are clean and have taken the DV apart again just to make sure there are no blocks. I've even start-filled the system with the DV off to double check there are no blocks, all is clear(just a bit wet). I'm fast running out of things to try, is it time to get a man in or just bite the bullet and buy a proper boiler? Thank's for all the ideas that have been thrown at me. I've certainly learned some new things.

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