Worcester Bosch 28CDi combi boiler hot water flow problem.

[noggo]

Hi all,

As there seam to be a lot more knowledgeable peeps here than me, so I thought I ask a question on behalf of a neighbour of mine whos been having problems with his hot water flow.

Combi boiler: Worcester Bosch 28CDi

The main problem is that when just the hot water tap is turned on (on any sink / bath) the flow is OK, but when both the hot and cold are running the hot flow reduces to a fraction of what it is without the cold running (quarter or may be less flow).

I have noticed that the hot water temperature does fluctuate a bit when it's the only tap running (no temperature monitoring equipment used, just me finger and it goes from not being able to hold your finger in the flow, too being able too).


I think there's a problem with the boiler, as my Worcester Bosch 280 isn't like that. OK there is a little bit of a drop off in flow, when both taps are opened but it doesn't drop off as much as his.

Any ideas anyone or shall I tell him to get someone in to look at it.

Thanks in advance for any replies.

Laters

Noggo

[mrgas]

Sounds like the mains stopcock to the property isnt fully open or is partially blocked.
Do you get the same effect when tryiny 2 cold taps?

[SteveZodiac]

My 28Cdi behaves similarly (although probably not as bad) and I had the diverter valve and water to water heat exchanger replaced a few months ago. I don't think my water pressure is what it should be though, and it does vary quite a lot. But if the water temperature is not steady at a given flow from just the hot tap there might be a problem with the boiler.

[noggo]

Thanks MrGas, you solved the one fault with hot water flow dropping off with adjusting the stop tap (it was nearly fully off). It drops off about the same as my 280 now .

Temperature fluctuations: an engineer was called and after doing some tests monitor gas usage when hot water was needed. He put it down to an Hot water temperature sensor. Which his going to get and fit there tomorrow or first thing Monday. I'll report back once it has been fitted, fingers cross he knows what he's doing and it solves the problem.

[noggo]

Well the new temperature sensor has been fitted and it has stopped the temperature fluctuations, but the hot water isn't getting hot enough. I didn't notice that the DHW temperature dial was set to maximum, yet you can still just about leave your finger in the flow from the hot tap. On mine on max you don't go near the hot tap flow, unless you're into self harm .

Anyways, the engineer has said the `water to water' heat exchanger needs replacing, does this sound right?

I would have thought it would have been the business end of the water heating `gas to water' exchanger would have needed de-scaling or replacing or may be even both. Any ideas anyone???

[bengasman]

Blocked secondary hex typically causes temperature fluctuation.
If the water is constantly too cold, you either have too much water flowing, or not enough gas.