Electrics and gas
How should a buyer separate microbore pipework, a cold radiator and sludge the survey did not flush when all three are mentioned together?
Keep the three apart. Microbore pipework is the narrow pipe the survey could see, a cold radiator is a radiator that was cold when it was checked, and sludge is a blockage the survey did not flush, so it was not shown. Narrow pipe is easier to block, but a cold radiator can also be air, a shut valve or a pump that was not running. The survey has not decided that sludge is the cause. It has named the pipe, noted the cold radiator and recorded that no flush was done.
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?
Microbore heating uses very narrow pipes, so corrosion debris that would pass a larger bore can stop flow in a short length. A cold radiator is a symptom with several causes. Sludge is one of them, and it is the one this visit did not demonstrate, because nobody flushed the system or opened a point where debris could be seen. The surveyor can trace a thin pipe to a cold panel. They cannot see inside the bore. The cold face is an observation. Sludge remains a possibility, not a finding.
Tell the solicitor the radiator was cold and the system was not flushed, so a heating engineer still has to find the cause. A power flush, if one is proposed, is that later job, not a result hiding in the report. Do not tell a lender the heating has failed from sludge. The survey did not test the boiler either. Gas work, if it is needed, belongs with a Gas Safe registered engineer. Keep the narrow pipes, the cold radiator and the unflushed sludge as three separate limits.
What should you ask your surveyor?
- Was the radiator cold with the heating called for, or simply cold on arrival?
- Were other radiators on the same microbore run also cold?
- Did you see sludge at a bleed point, or was none opened?
What are the typical next steps?
- Separate the narrow pipes, the cold radiator and the fact no flush was done.
- Ask a heating engineer to find why that radiator was cold.
- Do not describe sludge as confirmed.
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 microbore pipe itself a defect?
No. Microbore is a pipe size, not a failed test. It can block more readily than larger pipe when debris is present, but this visit did not flush the system and did not prove sludge. The cold radiator was a separate observation. The survey has not decided the pipework must be replaced. Size and condition stay different points.
Could the radiator have been cold because it was switched off?
Yes. A shut valve, a closed lockshield or a system that was not calling for heat can leave a radiator cold without any sludge. The survey did not flush the pipework, so it did not rule those out. Ask how the heating was set during the visit. Until an engineer runs the system properly, the cause stays open.