Dual Glow Worm Flexicom SX Boilers - F9 Fault Code

[Plumb Logic Ltd]

I have recently linked 2 no. Glow Worm Flexicom 30sx boilers and connected them via 35mm pipe work to a low loss header to serve an under-floor heating system in a large, new build, domestic property.

The boilers have both been suffering with a reoccurring F9 fault code which is taking them out of action at the same time. The client is currently resetting the boilers twice a day.

Glow Worm sent an engineer out who changed the pressure sensors on both boilers which made them work for approx 1 week before the fault started to reoccur.
I was skeptical about this fix as the heating system is newly installed, has been flushed and these two boilers only serve the under-floor heating.

Glow Worm sent out another engineer today who has said that the problem lies with the flow rate of water through the boilers.
Basically he thinks that the water is passing from the boilers and through the low loss header so quickly that the sensors in each boiler aren't detecting a pressure rise and are going to F9.
He has then simply closed the return isolation valve down on each boiler slightly in an attempt to "throttle" down the flow rate.

Does this conclusion and solution from the second engineer sound correct ?
Any advice much appreciated.

 

[ShaunCorbs]

tbh does it matter both boilers and are under warranty so if it doesn't work its not your problem unless there installed wrong, but if it does least you will know for future

and tbh i would never cascade two glow worms

 

[Chalked]

Are non return valves fitted to the the boilers, or are they seperately piped to the low loss header?

 

[ShaunCorbs]

Are non return valves fitted to the the boilers, or are they seperately piped to the low loss header?

should be separately and should be swing check valves

 

[Plumb Logic Ltd]

tbh does it matter both boilers and are under warranty so if it doesn't work its not your problem unless there installed wrong, but if it does least you will know for future

and tbh i would never cascade two glow worms

It matters because I am the first point of contact for my client when the heating system goes down and they are becoming increasingly, and understandably, annoyed and frustrated with the situation. I have now visited the property 3 times and Glow Worm 2. I just need to get this resolved once and for all and Glow Worms solution seems to be a bit of a shot in the dark.

 

[Plumb Logic Ltd]

Are non return valves fitted to the the boilers, or are they separately piped to the low loss header?

The boilers are linked before connecting to the low loss header and each boiler has a non-return valve on it's return as per MI's, see attached schematic from both Glow Worm & Vaillant.

 

[Plumb Logic Ltd]

should be separately and should be swing check valves

You cannot connect each boiler separately to a "Vaillant WH95" low loss header.

They are made with 2" BSP flow and return connections and are intended for multiple boilers to be linked via a common flow and return before connecting to them.

 

[ShaunCorbs]

You cannot connect each boiler separately to a "Vaillant WH95" low loss header.

They are made with 2" BSP flow and return connections and are intended for multiple boilers to be linked via a common flow and return before connecting to them.

View attachment 23589

No I mean the swing checks should be separate not the connections to the llh

 

[lame plumber]

glow worm are speaking the truth, I have had the same on a thermal store that starts pumping before the system boiler pump kicks in and the boiler doesnt see the pressure drop and throws up the fault. Best answer would have been to fit a better boiler in the first place....................