Ariston
Ariston Overheat Thermostat 999538
Overheat cut-out thermostat for Ariston Microsystem RFFI gas boilers, rated 100°C cut-out with 80°C reset.
At a glance
- Also known as OVERHEAT-THERMOSTAT-100C---80C, 1577686
Showing prices
£10.98
£9.15 ex. VAT · VAT at 20%
Available to order · 3 working days
Available to order · 3 working days
Not certain it's the right part? The technical team verifies fitment before dispatch — no charge, and it stops a second trip.Call the technical teamSend a technical question
Same-day dispatch
Ordered by 4pm Mon–Fri, 10:30am Sat.
30-day returns
Unused, in original packaging.
What it is
The Ariston 999538 is an overheat thermostat (overheat cut-out) for Ariston Microsystem RFFI gas boilers. It monitors boiler temperature and interrupts the burner circuit if the set point is exceeded, resetting once the temperature falls back. It is rated 100°C cut-out with 80°C reset.
Signs this part needs replacing
- Boiler locks out and requires manual reset, repeatedly.
- Overheat lockout occurs shortly after the burner fires.
- No heating or hot water despite a call for heat.
- Boiler cycles on and off more frequently than normal.
- Reset button trips again immediately after being pressed.
Before you order
- Confirm your boiler is an Ariston Microsystem RFFI model.
- Check the serial number falls within the ranges listed above.
- Match the GC number on your appliance data badge.
- Isolate the electrical supply before fitting.
Compliance
| Barcode / EAN | 5411692339982 |
|---|---|
| Alternative numbers | OVERHEAT-THERMOSTAT-100C---80C, 1577686 |
| Make | Model / assembly | Reference | Years | Fitment |
|---|---|---|---|---|
| ARISTON ARISTON MICROSYSTEM 10 RFFI - FROM SERIAL No 2320021100001 TO SERIAL No 2320024900001 | — | — | — | |
| ARISTON ARISTON MICROSYSTEM 10 RFFI - FROM SERIAL No 2320101600001 TO SERIAL No 2320106400001 | — | — | — | |
| ARISTON ARISTON MICROSYSTEM 15 RFFI - FROM SERIAL No 2320021100001 TO SERIAL No 2320024900001 | — | — | — | |
| ARISTON ARISTON MICROSYSTEM 15 RFFI - FROM SERIAL No 2320101600001 TO SERIAL No 2320106400001 | — | — | — | |
| ARISTON ARISTON MICROSYSTEM 21 RFFI - FROM SERIAL No 2320021100001 TO SERIAL No 2320030800001 | — | — | — | |
| ARISTON ARISTON MICROSYSTEM 28 RFFI - FROM SERIAL No 2320021100001 TO SERIAL No 2320030800001 | — | — | — | |
| ARISTON MICROSYSTEM 10 RFFI LPG EDITION 1 (AUG 2000) | 41-116-04 | 41-116-04 | — | — |
| ARISTON MICROSYSTEM 10 RFFI LPG EDITION 2 (FEB 2001) | 41-116-04 | 41-116-04 | — | — |
| ARISTON MICROSYSTEM 10 RFFI LPG EDITION 3 (FEB 2004) | 41-116-04 | 41-116-04 | — | — |
| ARISTON MICROSYSTEM 10 RFFI LPG EDITION 4 (SEPT 2004) | 41-116-04 | 41-116-04 | — | — |
Showing 10 of 34 compatible appliances.
Fitment listings are a guide, not a guarantee. Plant-room assemblies get modified on site more often than not. Send us the GC number off the data badge and a photo of the existing valve and we will confirm before anything is dispatched.
Documents & drawings
Everything we hold for this part. Where a document exists but we don't hold it, the technical team will source it from the manufacturer — usually the same working day.
manual
ARISTON appliance manual — MICROSYSTEM 10 RFFI LPG EDITION 1 (AUG 2000) (GC 41-116-04), MICROSYSTEM 10 RFFI LPG EDITION 2 (FEB 2001) (GC 41-116-04), MICROSYSTEM 10 RFFI LPG EDITION 3 (FEB 2004) (GC 41-116-04), MICROSYSTEM 10 RFFI LPG EDITION 4 (SEPT 2004) (GC 41-116-04), MICROSYSTEM 10 RFFI NG EDITION 1 (AUG 2000) (GC 41-116-04), MICROSYSTEM 10 RFFI NG EDITION 2 (FEB 2001) (GC 41-116-04), MICROSYSTEM 10 RFFI NG EDITION 3 (FEB 2004) (GC 41-116-04), MICROSYSTEM 10 RFFI NG EDITION 4 (SEPT 2004) (GC 41-116-04)
manualmanualARISTON appliance manual — MICROSYSTEM 15 RFFI LPG EDITION 1 (AUG 2000) (GC 41-116-05), MICROSYSTEM 15 RFFI LPG EDITION 2 (FEB 2001) (GC 41-116-05), MICROSYSTEM 15 RFFI LPG EDITION 3 (FEB 2004) (GC 41-116-05), MICROSYSTEM 15 RFFI LPG EDITION 4 (SEPT 2004) (GC 41-116-05), MICROSYSTEM 15 RFFI NG EDITION 1 (AUG 2000) (GC 41-116-05), MICROSYSTEM 15 RFFI NG EDITION 2 (FEB 2001) (GC 41-116-05), MICROSYSTEM 15 RFFI NG EDITION 3 (FEB 2004) (GC 41-116-05), MICROSYSTEM 15 RFFI NG EDITION 4 (SEPT 2004) (GC 41-116-05)
manualmanualARISTON appliance manual — MICROSYSTEM 21 RFFI LPG EDITION 1 (AUG 2000) (GC 41-116-06), MICROSYSTEM 21 RFFI LPG EDITION 2 (JAN 2004) (GC 41-116-06), MICROSYSTEM 21 RFFI LPG EDITION 3 (SEPT 2004) (GC 41-116-06), MICROSYSTEM 21 RFFI NG EDITION 1 (AUG 2000) (GC 41-116-06), MICROSYSTEM 21 RFFI NG EDITION 2 (JAN 2004) (GC 41-116-06), MICROSYSTEM 21 RFFI NG EDITION 3 (SEPT 2004) (GC 41-116-06), MICROSYSTEM 28 RFFI LPG EDITION 1 (AUG 2000) (GC 41-116-07), MICROSYSTEM 28 RFFI LPG EDITION 2 (JAN 2004) (GC 41-116-07), MICROSYSTEM 28 RFFI LPG EDITION 3 (SEPT 2004) (GC 41-116-07), MICROSYSTEM 28 RFFI NG EDITION 1 (AUG 2000) (GC 41-116-07), MICROSYSTEM 28 RFFI NG EDITION 2 (JAN 2004) (GC 41-116-07), MICROSYSTEM 28 RFFI NG EDITION 3 (SEPT 2004) (GC 41-116-07)
manualNo technical questions yet for this part.
Not sure which part?
Search by part number, product name or brand — our technical team confirms fitment before anything is dispatched.