Low Hot Water Flow Rate - Heat Exchanger?

[richie2305]

Hi,
I have a Worcester Bosch 24i RSF which has been installed for 3 years, and have noticed a huge drop in the DHW flow rate on all taps, (I know its cold but this wasn't a problem last year).

I have put a hose to the output of the Flow Switch and all seems ok, so this eliminates the supply/filter gauze/flow switch, but when I do the same after the Heat exchanger the water runs slowly, so my questions are:

1. Am I right in suspecting the Heat Exchanger or are there any little surprises ie filters in the circuit I can check in this area.
2. Is there an easy way to clean this, (I did run cleanser last year after the boiler made a knocking noise heating up).
3. If it is the heat Exchanger any advice on fitting, (I remember one post saying it was hard to stop leaks after, and I found this when fitting the DHW connection back on even though fibre washer in still there), for this reason the HW is isolated for now.

The CH seems ok apart from being slightly noisy when starting in the boiler, and we live in a hard water area.

Any help will be greatly appreciated, Thanks.

Rich

 

[ChrisR]

AH, waited long enough and there it was:

we live in a hard water area.

That's your problem. These are cr@ppy boilers and scale up for a pastime. They allow the HW to get too hot, so it deposits limescale just like a kettle does. Below 60° it doesn't happen. Much.
I know the fibre washer you mean - an unusual size, I 've had to make them before now.
Find the flow restrictor - little disc with a small O ring in the middle - if it hasn't disintegrated by now. Then find a bin for it. The increased flow rate which you should have got from day one means a lower temperature - until you turn the tap down.

Then you have to get citric acid (kettle descaler) through your boiler. You can connect to the boiler input, or heat exchanger, or a cold tap like a washing machine tap - with the mains stopcock off. Do obscene things with wifey's garden sprayer and you'll be able to attach a hose or plumbing fitting. Pump away and collect at a hot tap, and send it round again. You can warm the boiler on CH -go easy. WHen the hubble bubble stops you know there's nothing left to dissolve, so rinse well and have a go.
Let us know how it goes!

 

[richie2305]

Thanks for the reply Chris,

I went out and bought a Heat Exchanger today as I thought it would be difficult to de scale, so what I might do is clean the old one up for use when the new one gets caked in lime scale in another 3 or so years, the new one did come with some new washers so hopefully won't leak, I will add some PTFE tape as well.

I was wondering what the flow restrictor was for, especially as the flow rate is not that great anyway and no DHW temp controller, I will get rid of it.

I will also look into getting a Combimate softener to help protect the boiler from now on, a few people on this forum seem to recommend them.

Thanks again for your help.

Rich