Gas oil valve leaks should be repaired immediately. Contact a plumbing or heating contractor for assistance if necessary. Manual valves simply mean those that are operated by hand or wrench. Combination valves can be operated by hand but are also thermostat controlled. Missing valves should be installed so a means of shutting down the fuel flow is possible if and when necessary without shutting off the main building supply valve. Valves that are may include those that are broken, have broken or missing knobs or handles, etc. Repairs are recommended immediately for this item since a flammable fuel is involved. Contact a plumbing or heating contractor for assistance if necessary.