Do I need a new boiler?

[Stevie C]

I have a Glowworm Flexicom CX30. The hot water gets hot but then goes cold, it never really gets hot enough. If I leave a tap running, it repeats the hot cold cycle a couple of times before coming up with an F25 error. So, up to know, I have had the heat exchange plate off and cleaned (although it did not seem too bad anyway). I have had a MagnaClean filter fitted, the system drain and cleaner put in before draining again and putting in inhibitor. Still same fault. I put the boiler in diagnostic mode and it seems that the flow temp reaches 80+ degrees quite quickly, yet the water is no where near that. The return temp is much lower at about 30 degrees so I'm thinking the flow is not right but given the heat exchange didn't look bad, what else could it be (or could it be that I should change it anyway?). Heating has been pretty much fine up to recently when I get the odd F9 fault which I believe is water pressure, sensor or pump.
I'm at a loss and just had 2 kids trying to have showers which keeps going cold. Could really do without paying for a new boiler just before Christmas and Glowworm charge £275 for a fixed price repair which is more than I have atm. Help appreciated

 

[flameport]

Glowworm charge £275 for a fixed price repair which is more than I have atm.

but vastly less than buying a new boiler.

If it's repairable, get it repaired.
If not, then spend 10x more on a new boiler.

 

[Gasguru]

No one checked the pump?
Looking in the ports of a plate hex gives little clue to the condition...either replace of thorough acid cleaning is required.

 

[Stevie C]

but vastly less than buying a new boiler.

If it's repairable, get it repaired.
If not, then spend 10x more on a new boiler.

It is for sure although there are exclusions on the T's & C's which says 'Parts not included in our fixed price repair work are the main heat exchanger and expansion vessel.'
Is the main heat exchanger not the part that has been cleaned? It has been removed and cleaned with brick acid once before cleaner was put in the system and again afterwards when the system was drained before the inhibitor was introduced.
If I was confident that the money is well spent, I would go for it as it is much cheaper than a new boiler.

As for the pump, could it be a problem given the central heating is ok?

 

[muggles]

You're thinking of the secondary heat exchanger. Put brick acid into the primary heat exchanger and there won't be much of it left - it's aluminium. Glow-worm should give you some options including one which includes the main hex etc, payable monthly if that's easier for you

 

[Gasguru]

Pump maybe fine on heating but in hot water mode boiler may be trying to dump 3x the heat into the domestic hot water.

 

[Stevie C]

Thanks for the replies. I've woke up this morning to F9 error and had to reset the boiler to get the heating on. This fits in with the pump suggestion and as F9 is quite a recent fault, maybe a result of how the pump is getting worse?
Anyway, I think I'll give Glowworm a call and see when they can get out.

 

[hertsboilers]

@Gasguru and @muggles dose this model have a filter in?
F9 is the same as F75 on Vaillant.

 

[Gasguru]

I've only come across a couple and they behaved themselves.
Indeed pressure sensor/pump issues need looking at.