Hello from England. Blimey! I did a search on google re: HS38 and came across this, didn't realise it could be such an emotive subject! The reason I'm contributing was to let you know that as far as British gas go, they must genuinely think it works. I have a combination boiler and I am in a very hard water area my heating system as of late has been making very loud knocking noises. I am a British Gas customer and they have a scheme EnergyExtra 50 whereby you pay £2 a month on top of your normal bill, if you then have a problem with your boiler, electrics, plumbing or drains you pay a £99 flat fee which includes callout, parts, labour and taxes. This is unlimited per job. So if they have to visit 3 times and fit 3 parts to fix a problem you only make the one £99 payment even if the cost of the parts is £500 (they also give you for free a standby saver multi-socket plug and a remote electricity monitor which displays how much electricity your appliances are using as part of the scheme). As I said my heating has been knocking, so I called out my usual plumber who said it was probably scale and it might be worth a try putting descaler into the system which he did and as it only cost me 30 quid was worth a shot. However it didn't work, he said it could be the heat exchanger, which would cost at least £200 for the job. So I obviously invoked my British Gas deal which will cost me £99 tops. The Engineer called a couple of hours ago, he thinks it could be the pump or the heat exchanger. He is going to change the pump first, if this doesn't work he will change the heat exchanger. There is however a caveat, the heat exchanger gets changed the first time under the deal with no extra charge, if however in say two years time because of scale the heat exchanger needed changing again, if in the meantime I haven't taken any scale prevention action I would get charged the full price, if I do take some sort of scale prevention measure it would still come under the £99 flat fee scheme. The engineer did tell me about about the HS38 which British Gas will fit for £117, and he did recommend it (well he would wouldn't he?). To be fair this chap fixed my boiler before and for my £99 I had 3 visits including a system flush, a new pressure relief valve, new auto air vent and a new Control Board , which as my regular plumber quoted me £132 just for the Control Board parts only, wasn't bad! I definitely think British Gas believe the HS38 will reduce their costs. They are not a charity and they obviously think the risk of boiler damage from scale will significantly increase if the HS38 is not fitted, they don't force you to have it done they are just amending the terms of the Service Contract if you don't. Anecdotally the engineer told me he has one fitted and he barely has to clean his glass shower cubicle anymore. I am as tight as a gnat's arse, but when he turns up on tuesday to do the pump I think I may go ahead a get the HS38 even if the heat exchanger isn't the problem. If I do take the plunge I will report back the results at a later date.