Worcester Bosch 280 RSF heat exchanger clean

8 Feb 2009
Reaction score
United Kingdom
I'm wanting to remove/clean/refit the water to water heat exchanger on my Worcester Bosch 280 RSF boiler (suspect poor heat transfer, boiler cutting in/out on demand). I'm struggling to find a specific gasket pack for the job (it's old now and exchanger type changed). I'm wanting to know my chances of the original seals surviving the change and if they don't what size seals do I require?
Sponsored Links
That model is quite a rare beast these days. Unfortunetly you almost certainly will need new o-rings for that sort of job, the washers will just be standard 1/2 inch or 3/4 inch ones propbably but the orings will need to be genuine correct parts unless you are very very lucky with some that are near that size.
PS: it probably wont fix it anyway, personally I'd put up with it as it is while its still in one piece and save for a new boiler
Thought that might be the case. Like you say I think I probably am better off just putting up with it. Difficult part is saving for a new boiler!
Thanks for the advice.
Sponsored Links
If you knew what the actual problem was you might be able to chemically clean it in situ.

But even that could risk causing a leak at joints depending on what chemical was used.!

I suspect the problem is poor heat transfer in the water to water heat exchanger. CH works fine, problem is with DHW. When hot water is demanded the burner fires up but after a short while cuts out (demand light remains lit) then fires up again. I think the temperature on the primary side is reaching 70 degrees and activating the high temperature switch due to the heat not being transferred to DHW side.
It could be the switch I guess but I was thinking it more likely to be the exchanger based on age of boiler and researching other posts.
Is there any tests I can do to prove what the problem is and if it is the exchanger is a flush something I can do myself or would I need to get an engineer?


I've just had a quick read of other posts and it looks like I'd need to get somebody in to do a proper flush job. I Just need to work out whether the heat exchanger is the problem and if I want to spend money getting the system flushed rather than putting the cash towards a new boiler.

The only way to correctly diagnose heat transfer problems is to set the water flow to the rated output of about 11 li/min and measure the flow and return temperature on the secondary heat exchanger. Should be about 15 degrees if clean and the boiler circulation is normal.

That needs to be measured with a contact thermometer using K type thermocouples.

Thanks Tony, your good advise is greatly appreciated. I don't own a contact thermometer but there is no easy access to the inlet/outlet pipework anyway. I think I'm going to have to admit defeat on this one. I think the exchanger is the problem but anything I do might risk putting the boiler out of action and force me to buy a new one quickly which finances won't allow at the moment. I think I'm just going to have to tolerate the problem while researching/saving for a replacement. It's had a good innings!

Thanks again,

You just use the contact thermometer probes on the pipes to the secondary heat exchanger.


DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links