This first Edition of BG02 incorporates up-to-date information and best practices relating to the operation of hot water boiler plant; steam boilers are covered in a separate document (BG01).  
The first edition of BG01 included hot water boilers, but in response to feedback from users of the document, this separate guide for hot water boilers was created.  Guidance on the Safe Operation of Hot Water Boilers (Ref: BG02) is a guidance document intended to assist the designers, managers, operators, maintenance personnel and Competent Persons (CP) of new and existing low temperature and high temperature industrial shell hot water boiler systems.
NTRODUCTION
Guidance on the Safe Operation of Hot Water Boilers (Ref: BG02) is a guidance document intended to assist the designers, managers, operators, maintenance personnel and Competent Persons (CP) of new and existing low temperature and high temperature industrial shell hot water boiler systems including in addressing the following issues:
The safe and efficient use and operation of the boiler installation;
Determining adequate supervision and maintenance requirements (levels and competence) that are consistent with the installed plant and its location;
Reducing the likelihood of explosion or other dangers from events such as:
Loss of water;
Over-pressure;
Overheating e.g. due to excessive scale;
Using efficient boiler operation to avoid the excessive pressure/thermal cycles and load swings which can accelerate boiler fatigue or failure;
Having the proper treatment and monitoring of the system and boiler water to minimise corrosion and scale and avoid microbiological fouling (biofouling), as these problems can result in energy wastage, poor system performance, and the need for early replacement of plant and components.
Compliance with the various legal requirements, in particular that for periodic examination by a CP in accordance with a Written Scheme of Examination (WSE) for high temperature hot water boilers.
SCOPE
This document applies to all industrial hot water boilers (normally shell boilers), including mobile hot water boilers and waste heat boilers, that fall into the following categories:
Low Temperature Hot Water boilers (LTHW)
Boilers designed to operate below 110°C with a design pressure up to 16 bar gauge; and
High Temperature Hot Water boilers (HTHW)
Boilers designed to operate above 110°C with a design pressure up to 32 bar gauge.
These guidelines cover the types of controls and limiters necessary to ensure safe operation of various arrangements of fully flooded hot water boiler systems both ?110oC and >110oC.  The term MTHW has not been used in this document for clarity.
The following boilers are specifically excluded from the scope of this Guidance Document:
Steam boilers and water tube boilers;
Boilers with a capacity exceeding 37 MW nett rated thermal input;
Domestic and commercial boilers with a rated capacity less than 100 kW;
Electric immersion boilers, electrode boilers and steam coil heated boilers;
Hot water coil boilers.
However, just because these boilers are out of scope of BG02, this does not mean that the regulations and general principles in this document should not be applied where suitable and applicable.