The Church of England controlled the right to marry before 1837. The only legal exceptions allowed in the time period from 1754-1837 were for Quaker and Jewish weddings. The most popular way to obtain permission to marry was by publishing banns showing the intention to marry over a three week period in the parish of residence of the bride and groom. If they came from different parishes then the banns would be published in both. Marriage by banns had to take place in the same parish(s) where it was published.
A more expensive but quicker way of obtaining permission to marry was to buy a license from the appropriate Anglican jurisdiction. A license would allow the couple to marry in one of three parishes named in that license. The jurisdictions that could grant a license within the county of residence were the same ones that issued probates. (Start with the probate jurisdiction given at FamilySearch Maps or see the county of interest under Probates for further information.) Licenses were also granted by the provinces of York and Canterbury. If at any time you find that your ancestors were married by license, always search for the documents that were filled out before the license was issued: the allegation in the pre-1823 time period, the bond, and the act book entry (especially if there is no allegation). (See # 5 below.)
Spacing between children tended to be two years. If a woman were married at age 24 or 26, she would have about 15 years for child bearing after marriage. Accordingly, let us assume that you have found 5 children for what appears to be the same couple in one parish. There were no further entries for this couple for 5 years before what appears to be the first child and 5 years after the last one. Start with the assumption that they married in that parish some time between one year after the christening of the first child and four years before the first christening, or to be on the safe side you could search a total of 10 years to allow for christenings of children elsewhere. If the likely marriage is not found in that parish, was there at least a banns entry that indicated another parish to search (probably hers)? If the banns are not given in the same marriage register, check to see if there is a separate banns book for that parish.
Start with a marriage search at https://familysearch.org/search/collection/igi. Use only the Community Indexed IGI feature. If the bride’s surname is already known, search for this marriage by starting with the least common surname of the bride or groom.
British Vital Records Index and Other On-Line Sites. (See church records items 2-4 for details.
Search http://www.findmypast.co.uk/help-and-advice/knowledge-base/parish-records/marriages. This is a fee site but free to those using the computers at the FHL and famiy history section of the BYU library.
Marriage Indexes. Search the indexes outlined for the county of interest in the table, marriage indexes. Details on indexes not found at the FHL are in Jeremy Gibson’s Marriage and Census Indexes (FHL 942 D27gjh 2000), but first check Genuki to see if the county record office has released an online marriage index. Also try Price and Associates for England under Marriage Indexes.
Marriage Licenses. At this point, consider using marriage licenses as a general search tool for any missing marriage. The allegations and bonds have been microfilmed for most church jurisdictions within a given county. Typically, they will be filed in the FHL catalog under the name of the county and the subject of Church records and then titles such as “Index to marriage bonds”, “Marriage bonds and allegations”, or “(Name of the County) ecclesiastical court records.” Some are available on line at other sites such as http://www.britishorigins.com/.
In the case of the Chester Diocese, 1750-1837, BYU's Center for Family History and Genealogy has a project to put Bertram Merrell's Index of English Marriages online. This version compares the entries from the bishop's transcripts or parish registers with the license documents. The database is searchable by personal names and the parish of interest. For further details of which parishes are included and the current status of the project go to http://englishmarriages.byu.edu/
If a parish had peculiar jurisdiction, start your search for licenses in the FHL catalog under the name of that parish. The jurisdictions and whereabouts of licenses in England are listed in Jeremy Gibson’s Bishops’ Transcripts and Marriage Licences (FHL Reference 942 K23b 2001 with an older edition at BYU under Religion & Family History Reference CS412 .G52x 1983). The licenses issued in London by the Vicar General for those who resided in the Province of Canterbury or by the Faculty Office for a license to marry anywhere in England have also been filmed. Go to http://familysearch.org/catalog-search and use the "Film Numbers" feature. Type 375222 to see the collection for the Vicar General, and 355430 for the Faculty Office.
Radius Search. Map out a 10 mile radius of parishes as per the instructions under Church Records. However, instead of searching each parish in order as they radiate out from the center, start your search in the marriage registers of any market towns or parishes at cross roads where the couple may have met for the first time.