House in South Norwood


This house in South East London has recently been bought by our customers.  Finding a few recommendations for our services on the ‘Virtual Norwood’ local community website (thanks, whoever you were!) our customers asked us to specify and quote for a modern combination boiler based replacement for an old ‘heat only’ Gloworm boiler and hot water cylinder.  They weren’t best pleased because the Gloworm boiler had thrown in the towel within hours of them moving in, and the weather is not kind in late January.

Original cylinder and boiler in bedroom cupoard

Our clients wanted the most fuel efficient solution available, which meant equipping their boiler with weather compensated controls.

System was in need of updating

Vaillant and Viessmann arguably lead the way in weather compensated domestic boilers in the UK.  The Bosch group have had them for years abroad, but have only recently introduced a limited range in the UK.  Our first Vaillant weather comp excursion in 2003 was a bit of a nightmare, because it turned out we were one of the first installers in the UK to fit it and there were a few software issues, all satisfactorily resolved after a conference call on site with Vaillant’s German HQ (and some new hardware couriered over).

Vaillant’s latest weather compensation enabled controller is the VRC470, which came out in December 2011.  A natty little number in chrome and black, it does much the same as its forebears, but in a more elegant presentation, and simpler to use.

So what is weather compensation?  Now mandatory in some European countries (we are told), WC (as it will be abbreviated from now on) allows an already highly efficient boiler to adjust operating parameters dynamically according to the weather outside.

A high efficiency (condensing) boiler can change the state of the burning vapour inside (air and natural gas, for instance) into a liquid (water).  I does this by firing the fossil fuel at something cool enough to condense the water vapour in the fuel.  When there is this change of state from vapour to liquid, energy is released, which improves the efficiency of the boiler over standard types.

If we lost you there don’t worry, because in essence weather compensation is just an automated way of turning the boiler thermostat up and down in relation to the outside weather temperature.  When it is cold outside, we need very hot water in our radiators, when it is mild outside, the water in our radiators can be much less hot.  When the water is heated at lower temperatures, the boiler works more efficiently, because it is cooler inside the boiler and more condensation is produced.

Therefore it follows that if we could design a system that monitors the outside weather temperatures while we are asleep, out at work, watching the TV and surfing the internet reading this blog – it could control the boiler thermostat every minute of the day and ensure we were extracting the best value from the gas we use.  Weather compensation is this system.

It will also work well with underfloor heating, oil boilers and LPG boilers.  It is common on commercial buildings but has only really started being used on domestic dwellings in the UK around 10 years ago.

We are often asked whether it makes the house not as warm;  this is not the aim at all.  If the system is set up correctly, there will be no loss of room temperature.  In fact, it should deliver less ‘hotspots’ and give a more even form of heating, because the radiators tend to be cooler but on for much longer periods.

Vaillant VRC470 weather compensation controller in hallway

Anyway, while I have been writing this, the job has been completed so here is the completed boiler, relocated to under the stairs.  It is a Vaillant ecoTEC 831 combination boiler, fitted with a Spirovent Magnabooster² dirt separator (underneath).

New pipework and dirt filter


No photography prizes for this one. The bedroom can now be made bigger, and without the boiler and cylinder, wlll be habitable in the summer.....