ARISTON MICRO COMBI - LUKEWARM WATER

[K2harry]

Advice Please. Went to an Ariston Micro Combi problem which was noisey boiler when hot water demand was on and only lukewarm water. In my inexperience I went for faulty heat exchanger which cured the noise but not the fact that only lukewarm water is still produced. Heat sensors have also been changed. I read in the FAQs section that it could be the diverter valve 'letting by' I understand the term 'letting by' relating to the Gas Meter ECV but am not fully aware of the detailed workings of a combi and how a diverter valve can 'let by' Could someone explain it and is it possibly the problem?

If it helps the owner used to have the hot water setting on 2-3 then gradually put it up to maximum but now there is no difference

Be gentle on me, this is a great forum but sometimes inexperienced guys say the wrong thing and the knowledgeable ones come down on us like a ton of bricks!

Sorry one more thing central heating working fine

[cso30]

Hi,

To test the divertor valve, wait until the system is cold, run a hot tap, if when the boiler fires for hot water the flow pipe to the radiators gets hot you know the divertor valve is faulty.

If it is faulty the whole valve will need replacing.

[Gasguru]

Basics first...are you getting the correct burner pressure/gas rate? Does the burner modulate down or remain at maximum?

The MicroCombi has a bi-thermal heat exchanger and there is no diverter valve.

Have you checked the system pressure is around 1 Bar cold. Early versions had no pressure switch. Heat is transfered from system water to DHW within the heat exchanger.

Have you considered the DHW spindle may be incorrectly inserted into the pcb potentiometer. On many boilers it is possible to have the spindle 180 degrees out. Or perhaps the spindle is broken.

Have you checked for mixer valves letting by? (ie cold water passes from cold to hot even when the mixer is off). Isolate the cold feed under the boiler and check there is no flow at all hot tap outlets.

[K2harry]

Many thanks for the replies

Burner gas rate at max is 11mbar as per MIs, I did push it up to 15 and got hotter water but obviously then put it back to MI level.

Pressure is 1 bar cold

Spindle I think is OK. When I turn on hot tap the burner remains at maximum. when I adjust the spindle it then has an effect on the burner

All taps ie kitchen and bathroom produce same lukewarm water so have disregarded mixer tap valves letting by but haven't isolated under boiler to confirm. Will do that tomorrow.

Have just spoken to the owner again, sometimes the hot water goes cold and then back to warm

Just thought if one mixer valve is letting by it's going to effect all taps isn't it!

[bgs100engineer]

i take it by heat sensors, you have change the thermistors? when the boiler is on full tilt, that is with the hot tap open full, what its the burner pressure? does the gas valve modulate upto full gas rate and then back down when the tap is closed alittle? how about the pump? is it set on 3, what is its performance like?

[K2harry]

Ignorantly not thought about pump but having just spoken to owner he did say that although central heating works fine boiler does only come on for a few seconds then goes off, then back on again. Radiators do get hot though. Is this the pump not circulating hot water quickly enough?

[bgs100engineer]

yes it could well be the pump. i would of said.

[Gasguru]

cso30 wrote:

Hi, To test the divertor valve................

and

bgs100engineer wrote:

.....how about the pump? is it set on 3, what is its performance like?

and

bgs100engineer wrote:

yes it could well be the pump. i would of said.

Do the forum (and the OP) a favour and stop posting garbage.

The boiler does NOT have a diverter valve and the pump is only used for heating.

might I suggest you RTFM. I hope you don't repair boilers for a living.

[bgs100engineer]

oh very sorry gasguru.

[K2harry]

OK not pump then, however 'Agile' who has posted 000's of messages also suggested a pump not working may be the cause of lukewarm water on a Combi (posted 31 Jan 2007)

The last thing for me to try would be the mixer tap valves letting by, I hope it is and it will teach me to tick off the simple possibilities before I go digging around

Many thanks and I'll post my findings

[Dan_Robinson]

And what boiler was he referring to?

[K2harry]

Ravenheat RSF82 ET

I presume completely different workings to the one I'm hoping to sort?

[Bambergaspipe]

bgs100engineer wrote:

yes it could well be the pump. i would of said.

The pump circulates the hot water then does it???? Sorry I posted this after you had been torn to shreds...