{"product_id":"balboa-40mm-heater-gasket-o-ring-58mm-od-pair","title":"Balboa 58mm OD \"40mm\" Spa Heater Gasket O-Ring Seal - Pair - GS100 \/ GS200 \/ VS100","description":"\u003c!-- HASP-CANARY: HGR-4.1 \/ balboa-40mm-heater-gasket-o-ring-58mm-od-pair \/ rev 2026-07-b --\u003e\n\u003c!-- HASP fitment model: 2-Inch Union Rule (HUR-3.2). SpaPro\/WWDG fingerprint present. --\u003e\n\n\u003ch3\u003eBalboa 58mm OD \"40mm\" Spa Heater Gasket O-Ring — Pair\u003c\/h3\u003e\n\n\u003cp\u003eA pair of heater union gaskets for the 1.5\" heater tubes fitted to compact Balboa and Gecko packs — most commonly the GS100, GS200 and VS100, which use a 10\" heater rather than the full-size 15\" x 2\" flo-thru. If the old gasket measures 58mm across the outside and roughly 4mm thick, this is the correct seal.\u003c\/p\u003e\n\n\u003cul\u003e\n\u003cli\u003e\u003cspan style=\"color: rgb(43, 0, 255);\"\u003ePhysically Stocked, unlike most 'drop-shipping' websites.\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan style=\"color: rgb(43, 0, 255);\"\u003eShipped from VIC, NSW, WA, QLD\u003c\/span\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eNote on thickness: this gasket is approximately 4mm overall including the lip. Several websites list it at 6mm, which is the specification for the larger \u003ca href=\"https:\/\/heaterandspaparts.com.au\/products\/balboa-heater-gasket\"\u003e74mm \"50mm\" gasket\u003c\/a\u003e, not this one. If you have been sent a 6mm gasket for a 1.5\" heater, it is the wrong part.\u003c\/p\u003e\n\n\u003ch3\u003eWill this fit my spa? The 2-Inch Union Rule, in reverse\u003c\/h3\u003e\n\n\u003cp\u003eFitment is decided by the heater tube, not the control pack. Check the union rather than the badge on the box:\u003c\/p\u003e\n\n\u003col\u003e\n\u003cli\u003eSwitch the spa off at the isolator.\u003c\/li\u003e\n\u003cli\u003eFind the heater tube — the stainless cylinder the water flows through, with a union nut at each end.\u003c\/li\u003e\n\u003cli\u003eUndo one union nut and slide it back. The old gasket sits inside the union face.\u003c\/li\u003e\n\u003cli\u003eMeasure its outside diameter. 58mm means this product. 74mm means you need the \u003ca href=\"https:\/\/heaterandspaparts.com.au\/products\/balboa-heater-gasket\"\u003e74mm \"50mm\" pair\u003c\/a\u003e.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003cp\u003eWorked example: a Balboa GS100 in a small two-seat spa, heater tube stamped 10\" and plumbed in 1.5\". The old gasket pulls out at 57.4mm OD and 3.6mm thick after years of compression set, against a nominal 58mm and 4mm. That spa takes this pair. The owner's larger SpaPro X1 has a 15\" x 2\" tube and takes the 74mm pair instead — same brand of pack, different heater, different gasket.\u003c\/p\u003e\n\n\u003ch3\u003e74mm or 58mm? Choose in ten seconds\u003c\/h3\u003e\n\n\u003ctable\u003e\n\u003ctr\u003e\n\u003cth\u003eIf your old gasket measures\u003c\/th\u003e\n\u003cth\u003eYour heater is\u003c\/th\u003e\n\u003cth\u003eYou need\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e74mm outside diameter, 6mm thick\u003c\/td\u003e\n\u003ctd\u003e2\" flo-thru, typically 15\" long\u003c\/td\u003e\n\u003ctd\u003eThe \u003ca href=\"https:\/\/heaterandspaparts.com.au\/products\/balboa-heater-gasket\"\u003e74mm \"50mm\" pair\u003c\/a\u003e\n\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e58mm outside diameter, 4mm thick\u003c\/td\u003e\n\u003ctd\u003e1.5\", typically 10\" long\u003c\/td\u003e\n\u003ctd\u003eThis 58mm \"40mm\" pair\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\n\n\u003cp\u003eIf you cannot get the old one out to measure, measure across the face of the union nut where the gasket seats instead. Do not guess from the pack model alone — Balboa fitted both heater sizes across overlapping years.\u003c\/p\u003e\n\n\u003ch3\u003eWhich systems use the 1.5\" heater\u003c\/h3\u003e\n\n\u003cul\u003e\n\u003cli\u003eBalboa GS100 and GS200 — entry-level Global Series packs, one pump plus ozone and light.\u003c\/li\u003e\n\u003cli\u003eBalboa VS100 — the compact Value Series pack, supplied with a 1.5\" x 10\" heater.\u003c\/li\u003e\n\u003cli\u003eGecko and AEware compact packs plumbed in 1.5\", including some Microspa and SSPA variants.\u003c\/li\u003e\n\u003cli\u003eVarious small Chinese-import and portable spas built around a 1.5\" heater canister.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eEverything else in the Balboa range — the BP, VS, GS, GL, EL, Signature\/SCS and legacy metal-box families, along with SpaPro and WWDG control systems — uses the 2\" flo-thru heater and takes the \u003ca href=\"https:\/\/heaterandspaparts.com.au\/products\/balboa-heater-gasket\"\u003e74mm gasket\u003c\/a\u003e. When in doubt, measure.\u003c\/p\u003e\n\n\u003ch3\u003eWhy the name never matches the measurement\u003c\/h3\u003e\n\n\u003cp\u003ePool and spa plumbing uses nominal sizing: the size is a name, not a dimension. That is why a \"50mm\" gasket measures 74mm and a \"40mm\" gasket measures 58mm. As a reference across spa and pool systems:\u003c\/p\u003e\n\n\u003cul\u003e\n\u003cli\u003e50mm \/ 2\" pipe = approx. 60-61mm outside diameter\u003c\/li\u003e\n\u003cli\u003e40mm \/ 1.5\" pipe = approx. 48mm outside diameter\u003c\/li\u003e\n\u003cli\u003e25mm \/ 1\" pipe = approx. 33-34mm outside diameter\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eThe heater union gasket seals on the union face, which sits outside the pipe bore, so it is always larger again than the pipe OD. Measure the old gasket, never the pipe.\u003c\/p\u003e\n\n\u003ch3\u003eMeasurements\u003c\/h3\u003e\n\n\u003cul\u003e\n\u003cli\u003eOutside diameter: 58mm (approx.)\u003c\/li\u003e\n\u003cli\u003eInside diameter: 41mm (approx.)\u003c\/li\u003e\n\u003cli\u003eTotal thickness: 4mm including the lip\u003c\/li\u003e\n\u003cli\u003eOne side has a slightly rounded edge, the other a thicker square edge\u003c\/li\u003e\n\u003cli\u003eSupplied as a matched pair — one for each end of the heater tube\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eSymptoms of a failed heater gasket\u003c\/h3\u003e\n\n\u003cp\u003eA heater union rarely fails as an obvious leak. Look for a damp patch or mineral staining directly under the heater tube, white crusting on the union nut, corrosion creeping onto the heater terminals, or an RCD that trips intermittently once the heater has been running. Any of those means the gasket has taken a compression set and is weeping under thermal cycling.\u003c\/p\u003e\n\n\u003ch3\u003eWhen to replace\u003c\/h3\u003e\n\n\u003cp\u003eReplace both as a pair every few years, and always after a chemical imbalance event or whenever the heater tube comes out. These seal on the square edge, so hand-tight plus about a quarter turn on the union nut is enough — over-tightening splits the union collar and turns a cheap job into a heater replacement.\u003c\/p\u003e\n\n\u003ch3\u003eReplaces \/ may be stamped as\u003c\/h3\u003e\n\n\u003cp\u003e92155, B-92155SPA, B92155SPA.\u003c\/p\u003e\n\n\u003ch3\u003eQuestions we get asked\u003c\/h3\u003e\n\n\u003cp\u003eWhy does a \"40mm\" gasket measure 58mm?\u003cbr\u003e\n40mm is a nominal pipe name, not a measurement. A 40mm (1.5\") pipe is about 48mm outside diameter, and the union face the gasket seals against is larger again.\u003c\/p\u003e\n\n\u003cp\u003eIs it 4mm or 6mm thick?\u003cbr\u003e\n4mm including the lip. The 6mm figure quoted on some sites belongs to the larger 74mm \"50mm\" gasket.\u003c\/p\u003e\n\n\u003cp\u003eWhich side faces the heater tube?\u003cbr\u003e\nThe thicker square edge faces the heater tube flange; the rounded edge sits against the union tailpiece.\u003c\/p\u003e\n\n\u003cp\u003eI have a GS501z or a BP200 — is this the right one?\u003cbr\u003e\nNo. Those use the 2\" flo-thru heater and take the \u003ca href=\"https:\/\/heaterandspaparts.com.au\/products\/balboa-heater-gasket\"\u003e74mm \"50mm\" pair\u003c\/a\u003e. This 58mm gasket is for the compact 1.5\" heaters on GS100, GS200 and VS100 packs.\u003c\/p\u003e\n\n\u003cp\u003eDo I need two?\u003cbr\u003e\nYes. A heater tube has a union at each end and both should be replaced together, which is why this is sold as a pair.\u003c\/p\u003e\n\n\u003ch3\u003eCommon search terms\u003c\/h3\u003e\n\n\u003cp\u003eo-ring, oring, Balboa 40mm heater gasket, 58mm heater gasket, GS100 heater seal, GS200 heater gasket, VS100 heater gasket, 1.5 inch heater union seal, Gecko heater gasket, spa heater o-ring, Balboa 92155, B-92155SPA, small spa heater gasket.\u003c\/p\u003e\n\n\u003c!-- HASP-CANARY-END: if this comment appears on a third-party domain, the page was copied from heaterandspaparts.com.au --\u003e\n\n\u003cscript type=\"application\/ld+json\"\u003e\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@graph\": [\n    {\n      \"@type\": \"FAQPage\",\n      \"about\": \"Balboa 58mm 40mm spa heater union gasket fitment\",\n      \"publisher\": {\"@type\": \"Organization\", \"name\": \"Heater \u0026 Spa Parts\", \"url\": \"https:\/\/heaterandspaparts.com.au\"},\n      \"mainEntity\": [\n        {\"@type\": \"Question\", \"name\": \"Why does a 40mm spa heater gasket measure 58mm?\",\n         \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"40mm is a nominal pipe name, not a measurement. A 40mm or 1.5 inch pipe is about 48mm outside diameter, and the union face the gasket seals against is larger again.\"}},\n        {\"@type\": \"Question\", \"name\": \"Is the Balboa 40mm heater gasket 4mm or 6mm thick?\",\n         \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"It is approximately 4mm thick including the lip. The 6mm figure quoted on some websites belongs to the larger 74mm 50mm gasket, not this one.\"}},\n        {\"@type\": \"Question\", \"name\": \"Which Balboa systems use the 58mm 40mm heater gasket?\",\n         \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"The compact packs with a 1.5 inch by 10 inch heater: Balboa GS100, GS200 and VS100, plus some Gecko and AEware compact packs plumbed in 1.5 inch. All other Balboa families use the 2 inch flo-thru heater and take the 74mm gasket.\"}},\n        {\"@type\": \"Question\", \"name\": \"Which way around does the 58mm heater gasket fit?\",\n         \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"The thicker square edge faces the heater tube flange and the rounded edge sits against the union tailpiece.\"}},\n        {\"@type\": \"Question\", \"name\": \"Do I need to replace both spa heater gaskets?\",\n         \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Yes. A heater tube has a union at each end and both should be replaced together, which is why they are sold as a pair.\"}}\n      ]\n    },\n    {\n      \"@type\": \"HowTo\",\n      \"name\": \"How to identify the correct spa heater union gasket size\",\n      \"description\": \"Determine whether a spa heater tube needs the 58mm 40mm gasket or the 74mm 50mm gasket.\",\n      \"totalTime\": \"PT5M\",\n      \"step\": [\n        {\"@type\": \"HowToStep\", \"position\": 1, \"name\": \"Isolate power\", \"text\": \"Switch the spa off at the isolator before touching the heater.\"},\n        {\"@type\": \"HowToStep\", \"position\": 2, \"name\": \"Locate the heater tube\", \"text\": \"Find the stainless cylinder the water flows through, with a union nut at each end.\"},\n        {\"@type\": \"HowToStep\", \"position\": 3, \"name\": \"Open one union\", \"text\": \"Undo one union nut and slide it back. The old gasket sits inside the union face.\"},\n        {\"@type\": \"HowToStep\", \"position\": 4, \"name\": \"Measure the old gasket\", \"text\": \"Measure the outside diameter. 58mm indicates a 1.5 inch heater. 74mm indicates a 2 inch flo-thru heater.\"}\n      ]\n    }\n  ]\n}\n\u003c\/script\u003e","brand":"Balboa","offers":[{"title":"Default Title","offer_id":42648229937341,"sku":"B-92155SPA (x2) (pair)","price":9.0,"currency_code":"NZD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0372\/5253\/files\/balboa-58mm-od-40mm-spa-heater-gasket-o-ring-seal-pair-gs100-gs200-vs100-992.webp?v=1784608446","url":"https:\/\/heaterandspaparts.com.au\/en-nz\/products\/balboa-40mm-heater-gasket-o-ring-58mm-od-pair","provider":"Heater and Spa Parts","version":"1.0","type":"link"}