Our customers in today’s case study bought a ‘new build’ around 8 years ago, in the Redhill area of Surrey.

Interesting 3 storey townhouse


Inside, these properties are very spacious, and the rear elevations have got multiple Velux windows, L shaped lounges, very light and open.  Unfortunately, the developers chose to ruin their good work by fitting an Ideal iStor boiler.

Our customer had fortunately taken out a British Gas Homecare contract on theirs, but after years of visits including a protracted one from the manufacturer themselves, and having replaced every part, some more than once, plus a powerflush etc, they decided it was time to throw in the towel.

Over much of the heating season, they’d wake up to a freezing house and have to go up to the second floor and restart the thing.

Taking the covers off just reveals more in the way

No one was sorry to see this go.  NB: Just to confuse everyone, that is the cover of the new Worcester boiler leaning against the iStor.

The iStor is basically a system boiler connected to an unvented cylinder, all fitted within a large steel box.  There are some clever touches, like a very fast recovery cylinder coil, and the water is stored at a higher temperature than in a normal cylinder, and then cooled by a blending valve before it leaves the boiler.  This allows the boiler to store more thermal mass of stored hot water energy.

However, this boiler looks like a committee designed it, so just doing an annual service involves a significant amount of fiddly dismantling, which in our industry means it won’t get serviced correctly, because no one has allowed the extra time.

Just getting the thing out of the cupboard required an angle grinder, it just didn’t want to leave.

We suggested a Worcester Bosch i System boiler, together with a Worcester Bosch unvented Greenstore cylinder.  We sited the cylinder in the old boiler cupboard, and moved the boiler to a new position in a nearby loft area.  This necessitated tiling over the old flue, which the scheme architect had decided to make a feature out of…..

the old flue horizontal turret, four times larger than needed

Old flue covered up, new flue in position (just behind left hand scaffolding vertical pole)

The system was fitted with two zones of heating, we retained the zoning but fitted Evohome based control;  a single unit will control heating in two zones, and hot water.  We flush fitted the Evohome in the lounge, using a recessed power supply.



Honeywell Evohome was used- without radiator valves

Worcester Greenstore 250 litre unvented cylinder replaced iStor

Zone valves neatly set out. Does your cylinder installation look like this?

Worcester i System boiler in position

New vertical flue

New boiler finished. Reflex auxiliary heating expansion vessel tucked behind.  Note Worcester system filter bottom right and 3 pole safety isolation switch, as boiler is fitted remote from the main cylinder cupboard

Most boilers have a very small heating expansion vessel inside, typically between 8 and 10 litres volume.  This is designed to safely accommodate the expansion that takes place in water – in a typical heating system, the water is 5% larger when the heating is on!

The internal vessel is only big enough for around 8 modest panel radiators, and certainly not underfloor heating systems or ”school type’ tubular radiators with a high water content.

For the last couple of years we have been exclusively using nitrogen filled expansion vessels by Reflex, (a German brand) having found many of the Italian imported vessels have a very short life.  NB: Worcester Bosch boilers also use the same supplier inside.

All round the job went to plan, incorporating scaffolders, roofers and heating engineers, all supplied by us.

As a footnote, our customers were so impressed that Tim got a little present.

And the winner is…..