Seren Park Gardens in Greenwich is a development of 277 apartments that was completed in 2010. The property management had recently been taken over by Haus Block Management who employed building services consulting engineers, FLOH Consulting (FLOH). CEM was retained to maintain the boiler plant room, arrange and connect temporary boilers as all boilers had failed and undertake the refurbishment of the plant room.

The Issues

The existing boilers had failed – failure had been caused by water quality issues, poor design and poor installation.

Poor water quality and the introduction of hard water to the system has led to build up of deposits on heat exchanger surfaces within the boilers, the creation of hot spots and thereafter the gradual failure of boiler seals.  This had been exacerbated by the short circuiting of the primary circuit as the current existing design and installation meant that primary and secondary water was mixed before it could even be supplied to the secondary side therefore always elevating boiler return temperature.

To rectify these existing issues, it was necessary to replace some plant components and to reconfigure some parts of the existing installation.  Conscious of the age of the system and wishing to maximise the use of existing components and materials the replacement proposals are a balance of what was economically achievable and have been developed on the basis of replacement of any retained components during their normal life cycle.

The Works

  • Supply and install four new high-efficiency gas-fired Hoval UltraGas condensing boilers in lieu of four disposed units.
  • Modify existing boiler flue to provide individual connections from each boiler to the main horizontal flue header.
  • Reconfigure incoming gas service to suit boiler arrangement.
  • Reconfigure condensate disposal system to suit boiler arrangement, allowing for replacement traps and components.
  • Disconnect and strip out existing twin head primary pump set and associated invertors, setting aside for reuse by the client.
  • Replace the primary circuit to suit revised boiler positions and alternative means of circulation through them. Each boiler will be provided with a separate independent pumped shunt circuit with two-port shut-off. The logic will be that only the water required for the operation of the operating boiler(s) will circulate.
  • Install new concrete base for primary shunt pumps to match height of existing plant bases, dimensioned to suit new equipment.
  • Disconnect and remove existing horizontal low loss header and replace with new fabricated vertical header to suit dimensions and configuration shown on tender drawing.
  • Design, supply and install fabricated steel support framework for vertical header.
  • Connect each of the individual boiler shunt circuits to the primary loop and connect to reoriented header with flow at the top and return from the bottom.
  • Modifications to incoming mains water pipework.
  • Disconnect, decommission and remove existing Purotap Compenso water softener and associated pipework.
  • Disconnect, decommission and remove existing XPOT filtration system and associated pipework.
  • Supply and install new ENWA sidestream filtration unit with separate pumped circulation circuit to provide full treatment of the system water contents over every 24 hour period on a continuous basis. Note this is a filtration only unit since reaction media is not compatible with aluminium heat exchangers in existing retained Remeha boilers.
  • Supply and install new manual dosing vessel to allow ongoing treatment.
  • Relocate existing air and dirt separator from secondary return pipework to primary flow pipework as indicated on drawings. Allow for complete strip down and clean of unit prior to reinstatement.
  • Replace existing strainer on secondary side pipework within plant room with new.
  • Upgrade existing controls installations to accept all new components and overhaul operation of them, together with adjustment of all set points to provide the safest and most efficient operation of plant as possible. Refer to controls section for specific details.
  • Test and prove operation of the pressurisation unit, ensuring charge on each vessel is correct.
  • Test and commission existing secondary side pumps and confirm variable volume operation via pump DPS within control system.
  • Replace existing and supply new foil faced phenolic foam insulation to all pipework in plant room, including removable jackets to fittings and components and labelling throughout.
  • Removal and disposal of all redundant components from site arising from the works and presently within the plantroom, including the two dilapidated boilers which are not being refurbished.
  • Reconfigure pipework within plant room to accept temporary plant arrangement during works.
  • Undertake all associated builders works including but not limited to plant bases, fixings and supports.

Maintaining Service

During the time required for this extensive refurbishment, the lead times for parts, securing funding and finally commissioning, we had to maintain services to all the 277 apartments.

To achieve this, we installed temporary boilers in the car park. We had to install temporary hoses under a roadway and into the boiler room. Then a short shutdown of the heating system to install three prefabricated stool pieces to connect the temporary hoses – on the flow, return & gas to operate the system off temporary boilers. A temporary mains supply was run out to them for water supply if needed.  Three temporary boilers were installed on a long-term hire contract.


The boilers were commissioned by the manufacturer, as was the ENWA unit – the BMS controls and electrics were commissioned by Sphere Controls. Handover was early January. 2022 when the consultant attended, identified minimal snags that were rectified and issued a Practical Completion Certificate for the works. O&M Manuals and As Installed drawings were supplied.