Vaillant Boiler not igniting - S.97 F.75

[spudz]

Vailant ecoTEC plus 637 System Boiler
S Plan
Unvented Cylinder
Honeywell ST6400C controller
13 Radiators

Boiler not igniting - S.97 F.75

Boiler was working fine before 2 radiators were relocated during renovation.
Now boiler fails to ignite and gives s.97 then F.75 code.
System has been drained down twice to eliminate any airlocks and had a ‘mains flush’.
Pressure switch and expansion vessel have been replaced. Digital pressure reading seems to mirror the analog dial so appears accurate.

If I squirt some water in with the filling loop during startup (S.3), the burner ignites and the runs (S.4) for approximately 30 mins. Then the burner stops and boiler shows Status S7 (boiler overrun) for several minutes. Not sure if this is an issue or just dissipating heat as the heating system has reached its temp ?

Then when the boiler tries to fire up again during S97 (Water Pressure Sensor check) the burner fails to ignite with an F75 (No pressure rise detected) unless I squirt some water in via the filling loop. It then runs for 30 mins… the cycle above repeats.

Is S.7 normal when heating has reached temp?
Can anyone help troubleshoot S97 error?

Many thanks

 

[Johntheo5]

When you start the boiler normally then you should see the pressure gauge rise by around o.2/0.3bar, if it does, then possibly a faulty "pressure sensor" or a failing pump. When it's firing for say 15 minutes or so note the flow and return temperatures D40& D41 in the boiler menu.

 

[CountryFan]

S7 is pump overrun which a factory setting of 5 minutes is usual.

F75 can be a few things, but as above the boiler needs to see the increase from the pump

 

[spudz]

S7 is pump overrun which a factory setting of 5 minutes is usual.

F75 can be a few things, but as above the boiler needs to see the increase from the pump

Thanks for the S7 confirmation
Not seeing an increase in pressure on the digital display when the pump starts. Pressure switch has been replaced with genuine part and seems to report accurately when water is drained/refilled and as the heating increases and also accurately mirrors the analog gauge so I’ve ruled it out.
Expansion vessel was also replaced and is charged to 1.5bar.
Chief suspect was an airlock but the system has been refilled and bled twice and all 14 radiators are getting hot quickly with no cold spots (thermal camera).
Reluctant to blame/swap the pump at this point as system was working perfectly before the system was drained and radiator moved and fault started the next day.

 

[spudz]

When you start the boiler normally then you should see the pressure gauge rise by around o.2/0.3bar, if it does, then possibly a faulty "pressure sensor" or a failing pump. When it's firing for say 15 minutes or so note the flow and return temperatures D40& D41 in the boiler menu.

Thanks John, not seeing a pressure drop (see reply above) and reluctant to suspect the pump or the new pressure switch but don’t know where to go from here.
F&R around 72/58 (radiator temp control knob was set at 68)

 

[spudz]

I believe the builders plumber also reduced the boilers output (d0) but had no effect