Bosch Thermotechnology · Error codes
Bosch/Buderus SSB255-512 70 — Overheat Error
70
Overheat Error. Supply temp exceed the limit Checks: a- Check the pump to verify the flow circulation b- Check if the valves on hydraulic circuit are open c- Check the supply temperature sensor Remedy: a- Change the pump or restart it b- Open the valves on hydraulic circuit c- Verify that the temperature sensor has the correct resistance values. If values are incorrect sensor must be replaced. The table classifies it as blocking.
Applies to
This overheating code is displayed by the SSB control on SSB255, SSB399 and SSB512 models, as documented in SSB255/399/512 Installation Instructions, doc 6720818454 (05.2019), sections 6.1.1–6.1.2 (6720818454). Codes can differ between controller generations, so always check the manual that matches your unit.
- Bosch Thermotechnology Buderus SSB (85-512, discontinued)
- Buderus SSB85
- Buderus SSB120
- Buderus SSB160
- Buderus SSB255
- Buderus SSB399
- Buderus SSB512
Controller: SSB control. Source manual: 6720818454.
Why a code is not a diagnosis
An over-temperature code protects the heat exchanger or venting; it does not reveal whether the cause is low water flow, a failed pump, trapped air, fouling or a sensor fault.
Safe things to observe
- Note the code and whether rooms or hot water are still working.
- If you see steam, melted wiring or smell burning, switch the appliance off at its service switch and call a technician.
Do not
- Do not reset the appliance repeatedly while the cause is unknown.
- Do not remove covers or bypass any high-limit device.
How professional service helps
- A technician checks pump operation, flow, system pressure and the cleanliness of the heat exchanger.
- Combustion and safety devices are verified with an analyser and the manufacturer's procedure after any repair.
Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Parts and service
Parts commonly involved
These parts appear in the documented text for this alert. A code reports a condition, not a failed part — a technician confirms the cause by testing before anything is replaced.
Boiler sensors (thermistors)
Boiler sensors are small temperature probes, usually thermistors, that tell the control how hot the water and flue gases are so it can fire safely…
What a technician checks →
Service for this alert
- Gas Boiler Repair
Licensed gas technicians from ROMA Heating & Cooling diagnose and repair residential and light-commercial gas boilers across…
Every boiler part explained — what it does, how it fails and what a technician checks.
Documented for Bosch Thermotechnology Buderus SSB (85-512, discontinued).
Frequently asked questions
Can I clear this code myself?
Clearing a code without fixing its cause usually just brings it back. Note the code, check the safe items on this page, then call a licensed technician. If your appliance manual describes a user reset for this exact code and it stays away, no call may be needed.
Boiler locked out? Call with the alert text ready.
The brand, model and this alert are passed along when you request service online, so the technician arrives prepared.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
- SSB255/399/512 Installation Instructions, doc 6720818454 (05.2019), sections 6.1.1–6.1.2 · 6720818454 · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.