W-B 28i Junior slow hot water

[Joe]

It's about two years old, non-condensing, and recently is taking a long time to come up with hot water. It fires up about five or six seconds after opening the tap, then it's anything up to about five minutes before the water gets warm, not counting the time it takes to get to the tap. The more recently it has been used, the less time it takes. It doesn't seem to depend on the water flow rate. The red light is on the whole time, but it's difficult to tell from the sound how much gas it's burning. The CH pipes stay cold.

Does that ring any bells?

[Tom]

I have the same problem with a 24i, waiting with anticipation for helpful replies.............

Tom

[John Stumbles]

Is the water coming out at a dribble that's taking a long time to get through the pipework? In that case it's likely to be scaled up (if you're in a hard water area).

The non-condensing 24/28i Juniors have combined heat exchangers rather than separate plate heat exchangers and diverter valves so if the boiler is firing up straight away it must be heating DHW straight away: you should be able to feel the DHW pipework inside and just outside the boiler getting hot and follow the pipework getting hot.

[Joe]

No, sorry, it's running as fast as it did a month or two ago, when the problem wasn't there. I expect a slightly slower warm-up in winter, when the incoming water is colder, but this is excessive. As I say, if I use hot water again within half an hour, there's no problem, and the flow rate hasn't changed. It's almost as if there's a huge heatsink that has to warm up before the water gets any heat.

Not obviously. I did wonder where all the heat was going, and I must assume the burner is throttled back to minimum during the waiting period.

[John Stumbles]

If you watch the gas meter (clock dial) while someone else turns on a hot tap can you see if the boiler is starting up at a low rate and then getting to full rate much later?

[Joe]

That could be difficult. We have an old style meter literally on the floor under the stairs. I may get curious enough to try, but I assume I'll have to get the proverbial Man In to fix the boiler anyway. I was hoping to get some idea of the problem, as this seems a reasonably popular model, but it doesn't look as if anyone has seen this before.

[Tom]

Sorry Joe but our boiler has seemed to cure itself! I wont believe until we have at least a week of trouble free hot water supplies.

Tom

[Joe]

More information: I confirmed that no pipes get hot during the dead period, and being an electronics engineer, I gave the cabinet a few thumps was rewarded with a blinking 'computer crashed' light.

Turned off the tap, reset it and tried again. Again the pipes stayed cold, and the flue showed only a very slight heat haze. Then after about twenty seconds, the sound started to fluctuate slightly and then the pipe got hot.

So this looks like a flame-failure device fault. Does anyone know whether this is purely thermo-mechanical, or whether it's an electric valve and sensor? The latter would seem to imply that the computer crash was the result of a dodgy joint, and it might be worth reseating everything. I would assume if it's purely mechanical then it needs replacing.