Baxi Solo 2 40 RS Boiler switching off for HW

[Needafilip]

Have a problem with my Baxi Solo 2 40 RS boiler. Working fine for central heating but after firing up for a couple of minutes for the HW the boiler switches off before reaching water temperature. (Not a reset from overheating boiler just switches off).
I have changed the HW cylinder thermostat, and checked the timer is working correctly so can rule these out.
Suggestions on probable causes or other things to check.

Phil

 

[kevindgas]

diverter valve stuck (usually found in airing cupboard)

 

[Needafilip]

Diverter valves working fine watched and heard them open and close for both central heating and HW. Also left open with manual lever boiler still switches off.

 

[gas4you]

Could be the HW valve head has a broken microswitch.

As the boiler works ok for ch, it will be an external control fault on the HW circuit.

 

[Needafilip]

If the microswitch on the HW valve was broken would the valve still open and close via synchron motor? Because the motor does still open and closes the valve it just doesn't remain open long enough to heat the water.
Could this be a PCB fault?

 

[gas4you]

Yes. The synchron motor just opens and closes the valve. Once the valve has been opened it actuates the microswitch to tell the boiler to fire.

As said I do not believe this is a boiler fault.

 

[Needafilip]

Just so I understand this correctly.
When the HW valve opens via the synchron motor the rotation of the valve switches the microswitch to tell the boiler to fire. This does happen i.e. the boiler does fire and stays on for a few mins, which would seem to suggest that the microswitch is working correctly, if it was broken the boiler wouldn't fire at all would it?

 

[seco services]

what have you 1 of these

or 2 of these

 

[Needafilip]

There are two 2 port valves.

I have also fairly recently(2-3 months ago) changed the synchron motors on both of these, following a problem that came up during the last gas safety cert. The engineer doing the safety cert phoned to say that the boiler would not switch off he had to switch off the elec supply to the timer. I went to the property to investigate and one of the valves was stuck closed so I replaced both synchrons and the system began to work correctly again.
But for the last couple of weeks the boiler has stopped heating up the hot water, it fires up for a couple of mins then switches off.

 

[seco services]

i would check the motor and micro switch on the hw valve.
maybe the motor is relaxing and so coming off the miro switch.
check if you still have power on the brown wire to the valve when this happens.

if you do it proves the cyl stat is still calling for heat.

and you have lost power on the orange.

 

[kevindgas]

sounds like a blockage or trapped air in the hot water circuit, check the circuit with hot water only selected the valve lever on the end should be free moving if it is then check with a multimeter that you have 240v on the orange. if you havent then its a problem in timer or cyl stat

is the pump rotating properly? as it will possibly have more resistance when just doing water as heat rises and could be part gravity feeding round heating

 

[Agile]

I went to one just last saturday to replace the cylinder stat on the instructions of a colleague.

The boiler still only ran for a couple of minutes.

The lady hardly runs her heating and could not have noticed that was not working properly either.

I found the solder joint on one of the pins on the fan control relay was failed and going open circuit when it warmed up.

These PCBs are getting a bit pricey these days. I am glad we still have a good stock of them.

Tony

 

[Needafilip]

Agile

Few points:

This boiler has no fan?
The PCB just controls the pump overrun timing.
What do you consider pricey, I've found one for £30 at local plumbers merchant.
What model were you working on?

 

[Agile]

It was a Baxi Solo 2 with a fan!

The PCB has a retail price of about £125 !

Tony

 

[seco services]

i wouldn't be looking for the fault inside the boiler.
as agile said his problem was on both heating/hw yours is only hw
so i would be checking the controls as metioned before.