As a result, the language of the policy is the sole determinant of the insurer's liability. In support of this position, General Casualty relies upon Brodek v. Indemnity Insurance Co. of North America, 292 Ill.App. 363, 11 N.E.2d 228 (1937), Jennings v. Bituminous Casualty Corp., 47 Ill.App.2d 243, 197 N.E.2d 513 (1964), and Ohio Casualty Insurance Co. v. Southwell, 284 Ill.App.3d 1019, 220 Ill.Dec. 492, 673 N.E.2d 404 (1996), While the cases generally support General Casualty's contention that the court must look at the contract language to determine the insurer's liability, both the cases and General Casualty's argument have little bearing on the issue here, namely, what is the insurer's liability where it has acquiesced, even inadvertently, to an employer's apparent violation of the requirements of the Act by seeking to procure a workers' compensation insurance policy that does not provide coverage to a certain employee.         Brodek resolved a claim at law seeking to recover for an occupational disease.

4, 390 N.E.2d at 491; Matzen, 69 Ill.App.3d at 72-73, 25 Ill.Dec. at 559, 387 N.E.2d at 16; Old Mutual Casualty Co. v. Clark, 53 Ill. App.3d 274, 279, 11 Ill. Dec. 151, 154, 368 N.E.2d 702, 705 (1st Dist. 1977); Monarch Gas Co. v. Illinois Commerce Commission, 51 Ill. App.3d 892, 897, 9 Ill.Dec. 434, 438, 366 N.E.2d 945, 949 (5th Dist. 1977); Lewis v. Lewis, 48 Ill. App.3d 281, 284, 6 Ill.Dec. 577, 579, 363 N.E.2d 106, 108 (5th Dist. 1977); City of Chicago v. Nielsen, 38 Ill. App.3d 941, 947, 349 N.E.2d 532, 539 (1st Dist. 1976); National Tea Co. v. 4600 Club, Inc., 33 Ill. App.3d 1000, 1003, 339 N.E.2d 515, 518 (1st Dist. 1975); Ellingwood v. Ellingwood, 25 Ill. App.3d 587, 592, 323 N.E.2d 571, 575 (1st Dist. 1975); Allstate Ins. Co. v. National Tea Co., 25 Ill. App.3d 449, 462, 323 N.E.2d 521, 530 (1st Dist. 1975); Allstate Ins. Co. v. Horn, 24 Ill. App.3d 583, 588, 321 N.E.2d 285, 289 (1st Dist. 1974); Slavis v. Slavis, 12 Ill. App.3d 467, 474, 299 N.E.2d 413, 418 (1st Dist. 1973); Jennings v. Bituminous Casualty Corp., 47 Ill. App.2d 243, 249, 197 N.E.2d 513, 517 (5th Dist. 1964). 15.

In contrast, where a respondent attempts to avoid the vested rights of petitioner by use of a special defense such as equitable estoppel, he has the burden of proving his case by evidence which is "clear, precise and unequivocal." Jennings v. Bituminous Casualty Corp., 47 Ill. App.2d 243, 249, 197 N.E.2d 513. In our opinion, none of the authorities above reviewed are decisive of the case at bar.

The word may have reference "to a situation where, because of something which he has done or omitted to do, a party is denied the right to plead or prove an otherwise important fact." ( Jennings v. Bituminous Casualty Corp., 47 Ill. App.2d 243, 249, 197 N.E.2d 513.) Other definitions include in substance the concept of reliance by one party, to the extent of a change of position to his detriment in good faith, upon the conduct of the other as a result of which that other party will not be permitted to raise a contention inconsistent with his misleading conduct.

The party who asserts estoppel bears the burden of proof; that proof must be `"clear, precise and unequivocal.'" City of Chicago v. Nielsen, 38 Ill. App.3d 941, 947, 349 N.E.2d 532, 539 (1976), quoting Jennings v. Bituminous Casualty Corp., 47 Ill. App.2d 243, 249, 197 N.E.2d 513, 517 (1964). Windowmaster concedes that Safeco acted to its detriment by allowing payments from the trust fund and by paying Parnell.

No other evidence supports defendant's theory of acquiescence and it has thus failed to meet its heavy burden of proving this affirmative defense. See Jennings v. Bituminous Casualty Corp., 47 Ill.App.2d 243, 197 N.E.2d 513 (5th Dist. 1964).          Finally, defendant asserts that plaintiffs are barred by laches because they failed to object for eight years after they became aware of defendant's conduct.

The doctrines of estoppel and waiver would not have been of comfort to plaintiffs in any event. Waiver and estoppel are not available to extend policy coverage to risks that are not covered or that are expressly excluded therefrom. See, e.g., Jennings v. Bituminous Casualty Corp., 47 Ill. App.2d 243, 197 N.E.2d 513; Spence v. Washington Nat. Ins. Co., 320 Ill. App. 149, 50 N.E.2d 128; Travelers Ins. Co. v. Eviston, 110 Ind. App.143, 37 N.E.2d 310; Commonwealth Ins. Co. of N.Y. v. O. Henry Tent Awn. Co., 287 F.2d 316 (7 Cir.). This view is in harmony with the great weight of authority.

The party claiming estoppel has the burden of proving it by clear and unequivocal evidence. Jennings v. Bituminous Casualty Corp., 47 Ill. App.2d 243, 249 (1964); see 18 Ill. L. Prac. Estoppel § 36 (1956). Applying these principles to this case, we conclude that defendants' estoppel defense is meritorious.

Under the law of Illinois, as we find it, the doctrines of waiver and estoppel cannot be used to broaden the coverage of an insurance policy. Jennings v. Bituminous Cas. Corp., 47 Ill. App.2d 243, 197 N.E.2d 513 (1964); Spence v. Washington Nat. Ins. Co., 320 Ill. App. 149, 50 N.E.2d 128 (1943); Simmons v. Continental Cas. Co., supra; Commonwealth Ins. Co. v. O. Henry Tent Awning Co., 287 F.2d 316 (7th Cir. 1961). See, also, 1 A.L.R. 3d 1139 (1965).

Estoppel rests largely on the facts and circumstances of the particular case. Jennings v. Bituminous Casualty Corporation, 47 Ill. App.2d 243. It can be invoked as a defense against municipal corporations, as is being done here, if the necessary facts are established to warrant its application.