DIY Doctor UK DIY Forums

Thames Water recently did a 6 week upgrade of our street's water supply. They said it would increase our pressure.
Since then (3 weeks ago) our boiler has shut off twice due to low pressure, easily rectified by topping up with the filling loop.
Thames Water say it cant be due to their work and hence 'their leak', as the supply does not go direct to the boiler, and as there is still good pressure coming from the cold kitchen tap it must be internal.
Firstly is it impossible that an external leak would cause our boiler pressure to drop?
Our boiler is about 5 years old, the expansion vessel about 18 months, and the system well monitored. No issue before.
Only other thought was that if the water pressure had improved (though pressure wasn't an issue before and I see no noticeable difference), perhaps that is causing an internal leak on an unseen connection? There is no visible water damage inside.
It would be good to hear some expert opinions on this, as for me it is way too coincidental for the upgrade and brand new pressure issues not to be connected.
Thankfully it is only a small leak, but I can see this as being the start of a long journey to find and rectify it, and getting TW to take ownership.
Much appreciated.

Hi Adamcd.
It’s just not possible for an increase in mains pressure to cause your heating system leak. If you topped up after the mains pressure increase and overdid it, causing the pressure relief valve to operate, you may now have a leaking pressure relief valve. Have a look at the relief valve pipe and see if it is wet.
Regards S

Thanks for your reply. No the pressure relief is dry, and I topped up well within the parameters.
There is no leak internally anywhere that we can see, but are losing about .1 bar of pressure every day.

Hi adamcd,
In that case you may have to resort to one of the leak sealing additives.
Regards S

Thanks for the suggestion but that is a very last resort. Will likely invalidate any boiler warranty.
The leak is almost certainly external caused when TW upgraded the system as we never had an issue before. I’ll keep on with them.