Descaling Worcester 240RSF DHW

[Graham81]

Following on from a previous topic.

I have replaced the diverter valve in my 240RSF, as rads were getting hot whilst hot water demanded, and water from taps only getting luke warm. This did not resolve the issue, and now with advice from you guys I suspect the DHW is scaled up forcing the flow to open the shutter in the diverter valve and heat the central heating instead (as diverter is only flow driven, not motorised).

I want to attempt to descale the DHW without removal (if poss) but am worried that if the diverter valve is not operating properly because of the scale how will the descaler e.g. DS40 get to circulate the DHW to work its magic?

 

[Paul Barker]

Look, first of all congratulations on your demonstarted efforts and comprehension so far.

I am not an expert on this, actually I had a mind to talk to Tony off line and ask what his method is.

I'm finding my way in this trade. My mentor never descaled a heat exchanger in his life to my knowledge with 30 years in the trade and he's a good repair man.

Another guy/mate who was chief fitter for GAs fire place many years and is now irgi says you put your power flush on cold and hot pipes to and fro boiler and reverse direction many times, whilst using a suitable chemical. I am not sure that reverse flow is advisable on all dv's, can anyone help with this?

Isn't that heat ex a white cylinder? That's one good thing, not a plate one with 5 year obsolescence built in. I beileve they first appeared with a 5 year guarantee but when they found themselves changing them every year they went quiet about guarantees. That's how my Mentor put it, he had some choice ANglo Saxon descriptive expressions to say about plate heat exchaangers, but now they are here to stay, lucky you you don't have one. AFAIK only reason to have one is probably mss manufacturing yields cheap product and small product so boiler fits better in kitchen cupboard.

Brick cleaner is meant to descale, but I never tried it.

Old method was a certain dilution of hydrochloric acid, was it 1 part acid 4 water? But which way round do you put it in? Very important to do it right way round I know. Never done it.

Must be worth asking Worcester how much a new part is.

I took one of these out, and shame customer wanted to see inside his heat ex so took an (my) angle grinder to it, so all I could do was weigh it in. I can report however thet the tubules inside are about 10mm diameter so a heack of a lot more resiliant to scale than a plate heat exchanger.

I hope someone who knows what he's talking about answers properly.

Nothing to loose, if it were mine I'd take heat ex off, go to chemist to discuss hydrochloric acid properties/mixing/supply, bath it in the stuff for a few days oif necessary, render it safe with copious flushing, put it back and if it doesn't work I'd know it wasn't that part.

Boiler should still be a goodun.

 

[Paul Barker]

Stick with it, at the end of it all, which householder on this planet will know his boiler as well as you. Half of them don't know one end of a filling loop from a pantomime horse.

I'm now discovering that the people I gave a free call out to because all they needed to know was how to use their filling loop, have no memory of the conversation a year later, only now I've toughened up and charge them full call out. I;ve had to spend an absolute fortune out of my savings this year just to operate legitimately in the trade.

 

[ChrisR]

Graham there are quite a few posts on this sort of thing - which is easy to say I know, but do have a good dig.
Unless you're in a really hard water area the problem is much more likely to be sludge on the primary side of the dhwhe than limescale on the secondary side. Bad limescale woud reduce hw flow. Surface thermometry diagnoses - has been covered. The old type (like yours) dhwhe is more likely to be affected by limescale - the plate ones shed it when they flex, we're told.
This means that powerflushing won't touch it beause the HW circuit only operates when you have the tap running. Unless you isolate the boiler and turn the tap on - but with due regard for need for it to dump heat other than through the dhwhe - then your chemicals will be going into the main ch system. You could shut all rads except one, etc.. Must say that experience is crucial here to not get yourself into more trouble - there are many traps...
One option is to remove the dhwhe and pour desludging chems into it. If you had a powrflusher like we all have it's easy to just connect the thing up for a while.... They can go on washing machine taps for the tap water side alone, in situ. Never a quick job though overall.
Hydrochloric is nasty stuff, it also attacks things you don't want it to. I mean boiler parts, which are more important than skin - skin mends itself . Have to advise you Don't use it.
Citric (DS-40) works, but slower, as does Kamco FX-2 (citric + phosphoric). Have heard tales of less aggressive chemicals working but I'm not that patient. I HAVE used kettle descaler powder with success, surprisingly. The stuff for limescale is sulphamic acid (DS-3).
They all work better hot so pour boiling water into the secondary side, with enough descaler for whatever's in there.

You can always use two powerflushers - one on the washing machine taps to simulate the tap being on and clean the 2ndry side, the other connected where the pump goes inside the boiler .

 

[Graham81]

Thanks for the responses guys. I am an electronic engineer myself and an avid DIYer so am always keen to know how these things work.

I think I will wait until the weather warms up a bit, or until the boiler stops producing any hot water. (as the misses won't let me near it now as she says she can put up with it). Then I'll remove the DHW and clean it with whatever chemicals I can lay my hands on, and cross my fingers.

One other question. Is it safe to run the boiler with hot water demand with the CH flow shut off to get full heating ability, as long as the CH flow is then reopened promptly before hot water demand is ended so that excess heat can be dissipated in the CH system? Or will the boiler still overheat? Or is there a possibilty the pump will burn out if the DHW has restricted flow within it?

Sorry for all the questions.