BG 330+ v slow heating F22 error

[Giblets46]

Hi Just looking for some 'second opinion' or knowledge, as had someone round who failed to resolve the issue and is not clear on the cause.

So I have a BG 330+, it was serviced last October (including a flush of the heat exchanger). Wednseday morning noticed a lack of hot water the other morning (assumed the kids or partner had used it all), turns out more of an issue. My partner did note they had had a power cut (all the clocks rest) the day before (we seem to have them relatively often round here), not fuses were tripped though, so it may (or may not) be relevant.
I got home assuming something simple, and noted an F22 error (low pressure error). We have a gravity fed system with a tank,
so I checked the radiators had water in, and the tank in the loft. No problem. Alternatively online suggests the pump has died, which I didn't check.
So I called in the experts from a mid size local company.

Checked the above and agreed with my conclusions, also checked the pump which was running ok.
They managed to clear the F22 fault with a reset, but the boiler was heating very slowly (they also got another F22 fault later, but appeared to clear). Initially the pressure was reading 0.0 was eventually increased to 1.0 bar. The water through the boiler took 5 mins to raise a couple of degrees (and 20/30mins had not got over 55c (despite demand being set at 75), there was only a 2c different between the in/ out flow.

Gas pressure is also fine, also checked the thermistors, and checked the temperature externally. The guy said the boiler appeared to not be increasing gas flow and the fan was not coming on at a higher rate, so the boiler running at a lower heating rate. Clearly took a long time, with multiple resets and turning it on and off again (1 1/2hrs)

His suggestion is now that we strip down the boiler and clean out the heat exchanger, but appeared more in hope that anything. Anything else that is missing to check or something to keep in mind?
thanks

 

[CBW]

I'm confused, you state a feed and expansion cistern but a pressure reading too? Can you confirm which you have

 

[gazfen]

Pump

 

[gazfen]

Stuck valve

 

[gazfen]

Forget that it’s the pcb, I’ve had that fault before. Boiler thinks it’s a pressurised system when it’s an open vent. Pcb 100 percent

 

[Giblets46]

fused, you state a feed and expansion cistern but a pressure reading too? Can you confirm which you have

its not got a feed, but cistern, and cylinder.
Just been quoted £240 for a strip and clean of the heat exchanger (after £170 for the checks above).


I'd note last year I had a service which included a clean of the heat exchanger for £96

 

[gazfen]

does it have a filling loop or a tank. If it’s got a tank in the loft it’s the pcb that’s faulty. I’ve had it once when I was at bg

 

[Giblets46]

Thanks, yes tank in the loft

 

[ianmcd]

Vaillant fixed price repair is your best option, call them out you will get a 12 month warranty on the call out and the attending engineer will make sure he changes absolutely everything or loses his monthly bonus

 

[gazfen]

I’ve told you what part it is, if it says the pressure.

 

[Cal10]

Deleted sorry

 

[Giblets46]

Thanks for the reply, I have not had the F22 error since, but the boiler is still slow heating

 

[gazfen]

Pump

 

[ScottishGasMan]

A gas engineer working on the boiler should put it in high rate and then check the rate of gas it's burning, if this is low, and combined with F22 faults is a very strong indicator that the gas/air side of the heat exchanger does indeed need thoroughly cleaned out.

F22 is activated on these open vent boilers by not seeing enough of a temperature rise on the flow after ignition. This could be because of flow rate issue caused for example by the pump, or a lack of heat building up in the heat exchanger. A lack of heat building up in the heat exchanger will be caused when not enough gas is being burned, the boiler fan draws gas and air in to combust in the heat exchanger, when there is a restriction in the air movement through the flue ways or heat exchanger less gas is burned so less heat is produced resulting in a lower increase in flow temperature which would trigger the F22 fault intermittently.