How we find the cause.
We check the fault against the cistern components, the connections and, where the symptoms point that way, the drain. A running cistern is usually an inlet or outlet valve. Water at the base is usually a seal or a connection. A pan that backs up is a drainage problem wearing a toilet costume, and it needs a different job entirely.
When you replace a toilet, the existing outlet position, the set-out measurement and the water connection decide what will actually fit. Two suites that look identical in a catalogue can have different set-outs, and the difference means either pipework changes or a suite that does not fit. Check compatibility before you buy.
What to send us
Note whether the problem is constant or only happens during a flush, because that alone narrows it considerably. Photos of the toilet, the cistern and the connections help. If wastewater is backing up, stop using that toilet and avoid contact with the overflow.
What actually moves the price
The fault, whether parts are still available, access and whether you are repairing or replacing all affect the scope. For a replacement, confirm whether the price includes the suite itself, removing the old one and taking it away, because those are frequently quoted separately.