they have you there, if the tester is not repaired by an "authorised" agent/ repair centre then if you ever have any problems and testing/readings come out wrong, your insurance will be void if you ever need it or get accused/challenged due to a mishap caused by a possibly wonky tester...how would you prove that it was 100% functional if it had a diy repair and not signed off by the makers workshop...
A lot of different manufacturers PAT tester models heat up when used doing large volumes of tests like when in office buildings, and in the user manuals most of them say about a certain number of minutes between 500V tests etc to avoid damage/significant overheating to internals....
This is not very easy when you have a lot to do.....maybe it would be better to ask seaward for a price directly for servicing/component as its a 10 minute job but has to be done by a manufacturer rep to make it all legal and above board...
I force myself to delay between tests for a couple of minutes which is an inconvenience but I have felt the case on testers heating up like a toaster sometimes when sitting with a big pile of IEC leads to test and the likes...
£159.00+vat@ 20% is £190.80p then add £30.00 (and I assume vat onto that as well: £36.00) and you have it at £226.80p ......maybe it would be worth looking at buying a new machine instead as that's an awful lot for a £4 relay and a quick calibration, wouldn't be surprised if it takes about 15 minutes...
many of the PAT tester sellers offer a trade in of old machines, which they fix up, calibrate and sell on, and I can't see that they will add that much onto it if they are doing it for themselves to resell...
with testers, its always better to leave it to authorised registered repair companies to save any hassle.....if you do a good PAT test, and somebody else comes along behind you and hits it with a hammer/drops it in the sink or tampers with it, and somebody else comes along and plugs it in resulting in getting dropped and taken to hospital, then the insurance companies and HSE would look to blame you or me or whoever did the PAT testing even if it was 100% perfect when we left it....resulting in the taking of your records, pat training certificates, insurance documents and the test equipment you own/use including calibration certificates....if no recent calibration certificates are present and they open up the machine (expert witness etc) and find a self-repair, then you would likely get the blame and accused of incompetence due to malfunctioning test gear....then basically they would go for the neck and the old feet wouldn't touch the floor....
if all testers are serviced "in accordance with the manufacturers advice and by manufacturer authorised repairers" then you would have a nice official print out of service history and a calibration certificate, a bit like having an mot and insurance on a car.....and your insurance would be ok to pay legal fees to argue your side and prove you not liable...
if somebody gets any kind of shock from an appliance, even just a tingle, then that is quite dangerous for a lot of people, and will result in being taken into hospital overnight and connected up to monitors etc.....if somebody else causes this by making electrical equipment unsafe, then unfortunately the last guy that tested it is always the first point of call.....having all your records in good order is the difference between it being taken as an accident and going against the building owners insurance, or the tester getting hit for compensation and fees and no longer having the protection of an insurance company to save them... the H S E and the insurance companies always go for the quickest closure and the easiest route, which you don't want to be the target of...
I always make sure any safety critical electrical test equipment I use is calibrated and I keep any records in top shape as I know that without that I may as well just go round putting stickers onto everything in site without bothering as it would be just as bad for me...