www.ultimatehandyman.co.uk

I have a Vaillant ecoTEC Plus 832 combi boiler that was installed a few years ago. I've experienced this particular issue a few times so I'm wondering if there's a fault somewhere. This only happens when the central heating is on. Today I was running a bath (actually topping up the bath while I was in it - too much info?). I had the hot water tap on only. After a while the water started running cold and it stayed that way for about 10 seconds. It then recovered and ran hot again. It's happened before when I've been in the shower. My understanding is that when both hot water and heating are on it prioritises hot water - sensibly - and I take that to mean that the hot water tap should never run cold. It's not so critical in the bath but no-one wants the shower running cold.

Has anyone else experienced this? How can it happen? Does it sound like a fault?

Could be the plate heat exchanger is blocked with crud on the system side

gas4you wrote: ↑Thu Oct 10, 2024 5:57 pm Could be the plate heat exchanger is blocked with crud on the system side

Interesting. Would that happen on a 2/3 year old boiler? And why would it only last for 10secs or so?

Yes it could if the system wasn't properly flushed after installation.

The crud stops the heat transfer to the cold water so heats up the system side quickly. The boiler thinks it is up to temperature so shuts off. Then it cools and starts the process again.

gas4you wrote: ↑Fri Oct 11, 2024 3:07 pm Yes it could if the system wasn't properly flushed after installation.

The crud stops the heat transfer to the cold water so heats up the system side quickly. The boiler thinks it is up to temperature so shuts off. Then it cools and starts the process again.

Hmmm. The system was definitely flushed. I watched them do it.

Could be a faulty sensor, but that is rare on these