Intermittent Partial Filling of Tank
If the fill valve puts water into the reservoir every few hours this indicates that water is leaking through the flush flapper that neds to be replaced. If the fill valve does not flow water as soon as the toilet is flushed to refill the reservoir then the fill valve should be replaced. Both items are not expensive and are replaceable They can be purchased at Home Depot, Lowes, or any hardware or plumbing supply store.