Ariston Eurocombi sx20 mffice

[kjharry]

Hi,I am new on here,hope someone can help,I changed the pump pressure/flowswitch on one of these boilers a few weeks ago and it has gone again,tested the switch by bridging the switch and the boiler lit straight away so I know its the switch again but why would it pack in so soon?,or am I just unlucky to have a duff switch?,the water that came out of the boiler and switch were clean so I dont think its debris in there,no other work has been done on the system recently to disturb sediment.
I am Corgi reg before anyone asks,CCN1,CKR1HTR1,WAT1,CONGLP1PD,
CODNCO1,ICAE1,CIGA1,but I work mostly on commercial boilers,thanks.

 

[gas4you]

Rule 1 never think a part is good because it is new.

Is there any chance that a leak has dripped onto the external connectors and blown it?

 

[Gasguru]

Is the pin moving to actuate the switch?

 

[Agile]

If I remember correctly, on most of these models the flow switch is a moving magnet with an associated reed switch.

The moving magnet is probably not moving. They often get gunged up and can be cleaned.

Just sometimes the reed switch loses sensitivity.

Its not clear to me exactly what you have changed. Presumably the entire assembly?

Did you check the pump impeller to see if its blocked?

Tony

 

[DP]

As Gasguru suggests, check the spindle on the flow switch. Short circuiting the switch only prooves the circuit connected to the switch is working. Switch will only operate if spindle comes out, spindle will only eject if a) there is water in the system, b) it has been purged, and c) pump is running at correct speed.

 

[Gasguru]

If I remember correctly, on most of these models the flow switch is a moving magnet with an associated reed switch.

This is on the later Eurocombis with the plastic diff. pressure assembly on the front of the diverter. I have in the past found that brand new assemblies fail to work due to the reed switch being soldered in the wrong orientation on the small pcb. (the tines fail to close in the presence of the magnet)

On the SX20 MFFICE if there is insufficient differential pressure you may find the right hand connection onto the primary heat exchanger is partially blocked. Note you may need to double up a 3/4 fibre washer as the factory one is thicker than normal. You also need plenty of room on the RHS for spanner access.

 

[kjharry]

Thanks for all the help first,the unit is a small sealed unit screwed into the the pipe from the diverter valve to the heat exchanger,there is no moving pin to see,just three teminals with two wires connected,the third is spare,I have 240v to one side of the switch when the boiler is idle and should have 240v out of the switch when dhw or heating is called for but no 240v passes through the switch when either is called for,hence me taking the wires off and bridging them,boiler then lights.There is a small screw to adjust the sensitivity of the diaphragm and by turning this I can cause the switch make or break contact,checked with my meter for continuity,when installed under working conditions bog all moves it though.I know its this switch thats the problem but would another failing part on the boiler cause two of them to fail within a matter of weeks? or as I said is it just a duff switch?,tech help at Ariston said dirt in the boiler blocking the orifice into the switch,but it was as clean and clear as I could hope for,any thoughts?

 

[DP]

Look at the sequence of operation and not the switch (in isolation). The flow switch is a differential unit i.e., it senses difference of pressure in water created by the pump.

Just because the water is clear does not mean you cannot have particles that cause blockage. Have been to installations where the water was clear top of radiator but bottom was like tea cup with tea leaves. Blockage need not be at the flowswitch. If you look at the interconnecting pipes, or the aforementioned washer, it can be anywhere resulting in nonoperation of flowswitch.

 

[Agile]

What he is describing sounds just like a LP switch!

Dont remember ever seeing one on an Ariston and would not be on the flow out of the HE anyway.

If its the model with the grey boxed PCB just to the left of centre then that has the usual microswitch inside a rectangular plastic box operated by a pin from the front of the diverter valve. Earlier ones were on a stalk pipe towards back left.

Tony

 

[Gasguru]

That part is the presure switch on the right hand side. They are normally set to operate around 0.7 Bar (ie high for most pressure switches) and the screw on the back adjusts the switch point. Is the hole into the brass manifold definately clear? Perhaps the pressure gauge is defective and not showing the true pressure ie its reading higher than actually boiler pressure.

Probably looks like this...the CEME switch...normally very reliable (compared to the SIT)

 

[kjharry]

The picture posted by Gasguru is exactly right,it is called the pump pressure switch in the parts list but it actually senses the system pressure is over the minimum,to give power through it to the pump,fitted a new one today,boiler lit and is working ok,incidentally,the one I fitted today had two terminals instead of three but had the same part number,looks like it was just a duff switch,thanks.

 

[Agile]

The last 20 I saw failed were two leaking and 18 with the entry hole blocked!

Its better described as the system pressure switch but the Italians have some strange names for them.

Tony