Electrics and gas
Radiators are fed by microbore from the heat pump. Has anyone checked whether those small pipes can carry the flow?
No. Nobody on this visit checked whether those small pipes can carry the flow. The survey can see that radiators are fed by microbore from the heat pump. That is a description of the pipework in view. It is not a flow test, a balancing exercise, or a check that the emitters suit the pump. The survey has not measured efficiency. Approved Document L is energy-performance guidance for building work, not a result for these pipes. This visit has not issued a building-regulations certificate. The carrying capacity of the microbore stays untested.
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 is small-bore pipe used to feed radiators. Heat pumps generally move more water, at a gentler temperature, than many older boiler circuits. Small pipes can be a constraint. They can also be perfectly serviceable. The survey is not in a position to choose, because it did not measure flow, did not read a commissioning sheet, and did not balance the radiators. Seeing the pipe size is the start of the question. It is not the answer.
Ask the solicitor for any commissioning record or design note, and keep it separate from the survey. A heating engineer can test whether the circuit delivers what the pump needs. The survey does not decide grant eligibility and must not be asked for a grant figure. Tell a lender the pipes were identified, not proved. Do not describe the radiators as suitable because they warmed, if they were even switched on. Warmth is not a flow result.
What should you ask your surveyor?
- Was flow through the microbore measured?
- Is seeing the pipe the same as a commissioning test?
- Has this survey issued a building-regulations certificate?
What are the typical next steps?
- Treat the microbore flow as untested.
- Ask the solicitor for any commissioning or design note.
- Do not describe the pipe size as a passed test.
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
Does a noisy radiator prove the pipes are too small?
No. Noise can have several causes, and this visit did not investigate them or measure flow. The note is that microbore feeds the radiators from the heat pump, and that the capacity was not checked. Ask a heating engineer if the noise worries you. Do not turn a sound into a pipe-sizing verdict the survey did not make.
Could the system still work well on these pipes?
It could. The survey has not failed the circuit. It has said the check was not done. Small pipes are a question for design and commissioning papers, which were not read as a flow test. Approved Document L does not supply that missing test. Until an engineer measures the circuit, both success and failure stay off the page.