Boiler Hot Water Fault

Hard water area?

It sounds like it could be a sensor issue... what pressure does it report on its digital display on the front panel? Does that look comparable to that on the analogue pressure gauge next to the pump in the boiler?

First one to check would be the main service valve on the boiler itself. These boilers don't have flow regulation - they should deliver whatever you ask for, and modulate the power input to keep the water close to or under the set limit temp. In some cases installers use the input valve to limit the cold flow rate so that you can't get water delivered at below the temperature you want.

What flow rate do you get out of other cold taps OOI?

Yep. Don't think I can do much about it though.

I'm fairly sure it's soft (Sheffield) - no limescale for example. But it can vary by street and I've asked for a report from Yorkshire Water.

Yes, that's the one. 1.4 on the digital display, in the bottom quarter of green on the dial.

OK, thanks - I'll take a look at the service manual.

Very low - 3 or 4 litres/minute. It's only the garden tap and the new bath tap I've just fitted deliver 12 litres.

I agree with John that it could be a sensor issue although the fault in my Worcester Bosch results in water flow it just does not get hot. In my case the sensor is an impeller which detects water flow in the hot feed pipe and that fires up the boiler.

Could well be the sensor - mentioned as a cause of the F22 fault code. It's a cheap and easy replacement, but I wouldn't mind getting to the bottom of the poor flow through the boiler.

That is borderline for a combi TBH - even if it were all working correctly, the boiler would be able to outperform the supply rate in some cases.

If you turn the boiler off, does that change the rate of delivery of water from the hot tap?

No - still about 5L/minute. There's obviously something going on. I don't think it's the supply because the boiler inlet is fed directly from the main, and the garden tap (12L/minute) is a spur off the main, just before the boiler. I've checked all the valves, which appear to be open.

It's been like this since I moved in about a year ago, but only recently started cutting out.

Which to be fair is what I would expect - Vaillant combis don't usually include any flow regulation on the DHW.

Other than the plate heat exchange and a flow sensor there is not much in the flow path from the cold main inlet to the DHW outlet. So those would be worth checking... I suppose it is possible there could be debris stuck in the mains side of the inlet valve or a blockage in the feed pipe.

There is an EcoTec manual here: