Hydronic Heating

Most rooms have at least one hydronic heater panel (single or double plate) — some have two or even three (family room). The panels can be individually controlled.

The room controller for the heater is now a Siemens REV24 Programmable Thermostat but was a Landis & Gyr Chronogyr REV 10, 1992, no longer available. See below for a rundown on the REV24. The REV 10 has two set temperatures, day and night, as well as an ability to temporarily increase or decrease the current temperature setting until the next cycle. One of two programs can be selected with user-adjusted start and stop times. One allows two temperature changes per day, the other only one. The operating manual is here as a download (1120 kB, remove the '.sav' extension). A Siemens manual is also here to download (115 kB).

The heater room controller thermostat is set to 20°C for 'day' and 8°C for 'night'. Typically, the 'day' is set to start at 0640 and end at 2130. One program for the controller has the heater on 'night' setting from 0930 to 1600; the other stays on 'day' setting all day.

The boiler, expansion chamber and water panels are pressurised to approx. 1 bar when cold. This is about the minimum to force all air out of the panels upstairs when vented. The operating temperature is set to 60°C at the boiler thermostat, which leads to an operating pressure of about 2 bar.

Heater Electrical Diagram

Heater Maintenance

On 20 April 2010 we contracted Total Gas Care to give maintenance service to the Ferroli hydronic heater boiler (Model 5, Serial 6990). Seemed to operate OK after thorough clean out and replacing the temperature thermocouple.

Later inspection showed me that the water supply tap was seized, full of a copper oxide, the non-return valve looked blocked, and the pressure reduction valve was seized. The expansion vessel was also fully deflated so the air in the whole system was acting as the expansion vessel. No wonder I could not drain the air from the upstairs panels!

In May, I bought from Tradelink: ( Catalogue/09. Expansion Vessels & Accessories)

Flamco safety valve to suit the expansion tank, rated at 3 bar, in case the boiler overheats.
Flamco Flexfast Isolation Union to allow the pressure vessel to be removed without having to drain the whole system.
RMC EB35 pressure reduction valve 110–550 kPa, adjustable and set to about 120 kPa ( pressure set to be a little above the maximum elevation of the upper floor radiators - ie about 12 m)
RMC NR50 check valve.
Sundry fittings to make it all work, including a car tyre valve insert to replace the broken one in the pressure vessel.

Tests showed that the vessel holds pressure.

New Expansion Chamber, March 2012

Setting up the heater for the season showed that the pressure vessel had failed. The valve was leaking and there was a rust hole in the base of the vessel.

A new vessel, a Flexcon 12, was bought from Tradelink for $142.89. This vessel is 286 mm diameter, 332 mm height with a maximum working pressure of 3 bar - it is a little smaller than the original but big enough for the job. I set the air pressure in the vessel to 1.0 bar; this may need to be increased.

To set the pressure of the system, with everything cold I increased the pressure until no air was being expelled from the heater panel near the door in Bedroom 1. This required several iterations. The end result is that the pressure meter, which has a zero offset error, needs to read approx 1.1 bar cold.

Room Thermostat Repair

The Chronogyr controller is powered by two AA cells and these were leaking when we took over the house and had damaged the battery case connectors and two of the push button switches. Cleaning the area helped for a while, but the switches became progressively harder to use and a more permanent fix was required.

Two PCB switches (circled) next to the battery compartment were replaced with Jaycar SP0609 PCB mount tactile switches

The contacts (arrowed) for the battery compartment and nearby tracks were scrubbed with bicarb soda solution. Three applications of silver conductive varnish ( Jaycar NS3030) restored the electrical performance of those components.

The controller plugs into a mounting plate using three pins that pulse a miniature latching relay that in turn switches the mains voltage to the Ferroli heater. The pins are, from left to right: Common, On/Off, Off/On. These are wired to the relay, a Matsushita type DK1a-L2-3V.

Thermostat Replacement - Apr14

Attempts to start up the Chronogyr in 2014 have failed, so I have replaced it with a Siemens REV24 Programmable Controller. This is an updated version of the REV10, with a few unimportant extra features. I bought the unit from IPASSHOP on eBay for $195.00 delivered. The service from these people was outstanding, with extra setup instructions (important, since the Siemens instructions are not helpful when it comes to setting the PID control action - "PID self-learning"), and a laminated summary sheet. (Note that the price jumped $48.50 the day after I bought the unit.)

The setup and operating manual for the REV24 is here as a download (599 kB; remove the '.sav' extension to view).

LINKS

Hydronic Heater

A Dining Room hydronic heating panel — a double plate unit.

The 1992 Dining Room wall-mounted room thermostat controller for the heater.

Ferroli Hydronic Heater boiler in Laundry.

Inside the cabinet of the Ferroli Hydronic Heater boiler.

Above the Heater: the Expansion Vessel with its Isolation Union and Safety Valve on top on the right, electrical wall switch behind, and the water supply and drain on the left.

Detail of the plumbing: water supply to check valve, the pressure reduction valve, a tap to drain the system. The pipe in front is the from the safety valve on the Expansion Vessel.

Replacement Siemens REV24 Programmable Thermostat on the Dining Room wall.