Combi boiler fan/airflow fault

longwalks1

we’ve got a Worcester Bosch Greenstar 30i combi boioer, and the last couple of months the hot water temperature tends to fluctuate. I had this in an old home and had to run cleaner through it and clean (I think) the heat exchanger?
Yesterday morning no hot water at all but a C7 214 fan/airflow fault. Display temp on boiler was going up from 55 to 95 in the space of a few minutes when hot water was called for.

A quick google of the error came up with (unsurprisingly) fan fault, no fan power, faulty connections to the fan or a flue issue.

could it be the heat exchanger though? Had a gase safe guy round to look at it, said the fan is running and he said replace the heat exchanger - could the heat exchanger cause this fault?

just want to educate myself a little

FreeBear

If the P2P heat exchanger is blocked by sludge, water from the m\in heat exchanger wouldn't be able to circulate. The end result would be a rapid increase of boiler temperature and it would shut down. Not familiar with WB fault codes.. Possible that the logic board would flag it as a fan fault.

A blocked P2P heat exchanger would also explain a lack of hot water, but I would expect the water coming out of the tap to be slightly warmer than the cold.

longwalks1

thank you very much FreeBear

makes sense, sorry i should of said when there was no hot/warm water in the morning the boiler had already tripped out/failing to ignite.
when the temperature displayed raised quickly from 55 to 95 was when the engineer was here and we’d reset the boiler and was running the hot tap (which did supply hot water until it tripped)

WIAWSNB

Have a 'chat' with WB and see what they say.

There are two heat exchangers in (most) combi boilers, including the WB. The MainX - the 'engine' - is where the burner is located and hence also the fan, and this heats the system water for your radiators and DHW.

When the MainX heats the DHW, it does this via the second exchanger, the 'secondary' or Plate-to-Plate exchanger. In essence, this has a series of separated plates and water channels, with the heated water being passed through one set, and the cold mains water through the other, which is heated and passes out the boiler as your DHW.

So, what's going on here? No idea, because the symptoms and error codes don't add up.

When a P2P exchanger blocks up - a common issue if your system water has sludge in it - the classic symptom is the that DHW initially runs hot, before then going cold for some time - typically 30 seconds or so - before becoming hot again. It 'cycles'. It does this because the partially blocked channels don't allow enough hot flow through it from the mainX, so the mainX output overheats. A sensor detects this and shuts off the burner until the flow cools. Usually this is a temporary measure, and the boiler doesn't actually 'lock out' like yours has done necessitating a reset, but just fires up the burner again once cooled. Your boiler has actually locked out.

The fan is what draws in air and blasts the flame through the mainX. If this becomes faulty, the boiler may well shut off as it knows it's a serious problem that won't allow proper combustion. So, yes, nothing will work in this case, not the CH, and not the DHW.

Once you reset your boiler, the temp shot up quickly to 95oC before the boiler locked out? That tells us - suggests - that the mainX (the fan and burner) is actually working ok as it's clearly producing hot water as it should. However, it's clear that this hot water isn't being used up quickly enough, hence it overheating.

What prevents the heated water from being 'used up'? It could be a blocked P2P, but I wouldn't expect the boiler to lock out. It could be a faulty diverter valve, but usually ditto (unless it doesn't move at all). My boiler did recently lock out due to instantly overheating water, and this was due to a failed pump; no water flow = instant overheated water (accompanied by bangs...).

So, your symptoms aren't consistent.

I hope that helps 😛

Q - what happens if you run your rads? Does everything work ok?

Try that for 20 minutes or so, until the rads are nicely hot. Everything tickety boo? If so, that suggests your 'boiler' is fine - mainX, fan, burner, pump. Now turn on a hot tap. If the boiler now overheats and even locks out, it suggests a DHW side issue, so sticky diverter valve, or blocked P2P.

How old is the boiler? Would a WB fixed price repair make sense? They usually replace everything that's remotely dodgy, so is usually good value.

longwalks1

Belated thank you WIAWSNB

sorry I should of said the first morning the boiler actually locked itself in fault, the CH had come on early hours (we had a cold night and the UFH and CH comes on 4am to warm the house) so the CH had been on for 3 hours before I noticed no hot water and the locked out fault code.

Boiler guy has been round and replaced the P2P heat exchanger and the gaskets on the cylindrical heat exchanger (I think, metal barrel shaped component) too. All seems to be fine now, so thank you all for your help and answers.