Electrics and gas
What did the visit record about a primatic cylinder, about the header tank, and about a single-feed arrangement the survey named but did not test?
The visit recorded a primatic cylinder, a header tank and a single-feed arrangement, and it recorded that the arrangement was named rather than tested. A primatic cylinder is an older single-feed indirect cylinder that relies on an internal air seal to keep heating water and tap water apart. The surveyor could see the cylinder and the header. They did not test that air seal, did not run the taps as a performance check, and did not decide that the seal is still holding. Identification is not a working test.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
On a single-feed cylinder the header tank fills the unit, and a pocket of air is supposed to stop the primary circuit mixing into the hot water you draw. If that pocket is lost, heating water and domestic water can mix, and the header can behave oddly. None of that is visible from the outside of the cylinder. Seeing the primatic label, or the single pipe from the header, tells you the type. It does not tell you the air seal is intact. The visit stopped at the name.
Tell the solicitor the cylinder was identified and not tested. A heating engineer can check how this single-feed arrangement is actually behaving, which a home survey does not do. If the appliance is gas-fired, that check belongs with a Gas Safe registered engineer. Do not assume the header tank being present means the air seal is sound. The survey has not decided the cylinder is failing, and it has not cleared it. Any replacement is a later specification, not a result of this visit.
What should you ask your surveyor?
- How did you recognise the cylinder as primatic rather than a conventional indirect unit?
- Was the header tank shared with the heating, or did you only see one feed?
- Did you see discoloured water, or was the single-feed note only visual?
What are the typical next steps?
- Treat the primatic cylinder and header as identified, not tested.
- Ask a heating engineer to check the single-feed arrangement.
- Tell the solicitor the air seal was not proved either sound or lost.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Is a primatic cylinder the same as an unvented mains cylinder?
No. A primatic cylinder is an older single-feed unit fed from a header tank and an internal air seal. An unvented cylinder is fed from the mains and has its own safety controls. The survey named the arrangement and did not test it. Do not brief an engineer with the wrong type. The header is part of this note, not a mains-pressure system.
Does a full header tank prove the air seal is intact?
No. The header can look normal while the internal air seal has already been lost, and it can look odd for other reasons. The survey saw the tank and named the single-feed arrangement. It did not test the seal. A full tank is a water level, not a working test of the cylinder.