Potterton Envoy

...BOUGHT

The Potterton Envoy has a neat wall-cupboard sized casing, and can have a side- or rear-exit flue which is fan assisted. To look at this diminutive boiler and think it heats a 4-bedroom house would not have been credible a few years ago. The hole for the flue can be cut in one shot, by the installer, without the need for messy chiselling and with minimal dust.

INSTALLATION

Then the fitters turned ...
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Since the Potterton needed a +11C difference between its two pipes, it was using the –11C difference as a valid reason for shutting down.

So the awful truth was out. MY PREVIOUS SYSTEM HAD BEEN WORKING THE WRONG WAY ROUND FOR 15 YEARS, with the boiler’s natural convection working against the direction of the pump. No wonder it got through pumps quicker than expected!

One look at the upstairs piping brought ... more

Firstly, let me say, for the benefit of those English-speakers on the other side of the Big Pond, that what I call a “boiler” is more likely to be known to you as a “furnace”. Right, that’s got that out of the way.

I have decided to completely rewrite this old opinion to reflect a period of what I hope is now “reliable middle age” for this boiler.

HISTORY: WHY WE CHANGED OUR BOILER

About three years ago, as I retired early, we drew up plans to revamp the kitchen, involving repositioning the boiler. You can guess from this, who was going to be doing most of the work!

In view of the age of the old boiler (that’s the water heater hung on the kitchen wall, not my wife!), we decided to budget for changing it instead. Fortunately, this was one of the jobs we knew that we wouldn’t (nay, mustn’t) tackle.

Being a sucker for something new or more complicated, I started to get interested in CONDENSING boilers, and went down to the British Gas showroom (yes, they still had them then!) in Hounslow to talk to them

I had heard of the benefits condensing boilers, but thought that they were bulky.

It seems that, along with a lot of other people, I was confusing the terminology with COMBINATION boilers, which really are bulkier, by virtue of the fact that they are not only a central heating boiler but an instantaneous hot water heater too.

Apart from this misconception, it appeared that I knew more about the damned things than those in the shop! Perhaps I should have taken this as a sign.

Anyway, a salesperson with what seemed to be a lot more know-how visited our house, surveyed the kitchen, and gave me some pre-requisites to have done before the new boiler was fitted. One of these was to divert the mains (electrical that is) supply to the site of the new boiler. This I duly did.

WHAT WE BOUGHT

The Potterton Envoy has a neat wall-cupboard sized casing, and can have a side- or rear-exit flue which is fan assisted. To look at this diminutive boiler and think it heats a 4-bedroom house would not have been credible a few years ago. The hole for the flue can be cut in one shot, by the installer, without the need for messy chiselling and with minimal dust.

INSTALLATION

Then the fitters turned up. “Who told you to put this mains supply here? – this is no good, it’s only got three wires. We need five”

So my nice new fused spur switch (with neon) was useless, until I diverted the supply to the garden shed through it, that is! So some good came of it, as I can now isolate the shed without tripping the understairs circuit breaker.

Fortunately at this stage, the wall was in a state of “undecoration” so no real harm was done.

Everything was fitted; the hole for the flue had been made with minimal dust, the boiler bolted to the wall and connected to water, gas and electricity. All ready now for test.

“OK, switch on,” says one. “I have” says the other, “but it keeps turning itself off again”.

After some head scratching, it was discovered that what we thought was the “return” pipe was in fact hotter than the “flow” pipe.

Since the Potterton needed a +11C difference between its two pipes, it was using the –11C difference as a valid reason for shutting down.

So the awful truth was out. MY PREVIOUS SYSTEM HAD BEEN WORKING THE WRONG WAY ROUND FOR 15 YEARS, with the boiler’s natural convection working against the direction of the pump. No wonder it got through pumps quicker than expected!

One look at the upstairs piping brought sharp intakes of breath, and worrying murmurings along the lines of “it’ll all have to come out”.

However, one of the fitters turned out to be a little diamond. The next morning, he turned up full of the joys of Spring, saying that he’d worked out how this “wrong-way thing” could be altered just by adding in one more piece of pipe, and by turning the pump round. Pipe was something we had plenty of, since the salesperson/estimator had gone a bit mad on the requisitioning of copper bits.

An hour later, we were all running again, and for the first time in 15 years, I didn’t have to turn off the upstairs radiators when I was only heating water for a bath.

WHAT’S SO SPECIAL ABOUT A CONDENSING BOILER ANYWAY?

Condensing boilers retrieve a large proportion of the wasted heat, which normally disappears out of the flue in the form of hot exhaust gases. Before it actually escapes to the atmosphere, it is forced to pass over a secondary water jacket, through which the cooler water, returning from heating the house, flows.

This warms the returned water up a bit more, making reheating it in the main jacket less thirsty for fuel. These boilers can actually be 95% efficient compared to about 75% for any ordinary one. In warming the water, the gases get colder, making them “condense”, separating out into a mildly-acidic “soda water” of CO2 dissolved in water.

The thermal efficiency doesn't end there. The outside case of the boiler is also very cool. Unfortunately, if you relied on residual heat from your old boiler's casing to heat the kitchen, make other plans with this one.

Also, because of the cool nature of the final exhaust, be ready for plumes of steam emanating from the side of your house on cold days!

The only peculiarity in installation (apart from 5 wires that is! Grrrr!), is that you need a separate slim-line drain pipe for the condensate to dribble through, and this shouldn’t be run outside of the house, through a wall say, in case it freezes in winter, causing a back-up of liquids in the boiler.

PURCHASING & RUNNING COSTS

The extra cost of buying a condensing boiler - (the twin jacket cores have to be made of aluminium and not cast-iron, to prevent the mildly acidic condensate from rotting the metal) WAS* partly offset by a grant from The Energy Saving Trust, since I was helping the government meet its CO2 reduction targets.

*I believe this grant has been discontinued.

I kept an Excel spreadsheet of comparative readings between previous years and those subsequent to the new boiler being installed, and we seem to be burning about 25%-30% less gas. This is in excess of the claimed savings, but bear in mind that the old boiler was probably not at its most efficient when we got rid of it.

PROBLEMS

The boiler was totally reliable for over a year in operation.

However, just before Christmas 2000, it started blotting its copybook.

23/12/00 – Boiler not lighting. Maintenance man calls, but concludes he will not get the parts he needs till after Christmas – lucky for us that we’re going away!

6/1/01 – Maintenance man returns. A water build-up in the combustion chamber was short-circuiting the ignition. This was at first thought to be too much condensate building up inside because of sludge blocking the pipe which siphons away the acidic water. New igniter fitted, boiler dried out and re-lit.

22/1/01 - The above still not resolved, the water build up persists. To everyone’s surprise, the water has been coming from a crack in the primary heat exchanger. By replacing this, British Gas has almost replaced the complete innards!

This still left a minor clean water leak to be sorted out, which was diagnosed as a faulty combustion chamber casting, and had to be put on hold while the makers supplied one.

01/03/01 - the new combustion chamber was fitted and the leak stopped just long enough for the technician to get out of the door! I then did some detective work of my own. Using a step-ladder, I was able to see a puddle atop the boiler.

This last leak was found to be condensation dripping from the rubber collar that links the top of the boiler to the flue. It seems to me that the fitters hadn’t quite got the flue pipe dead-centre over the boiler, putting some sideways strain on the collar, which in turn affected the water-tightness of the fit.

The BG man had failed to spot it (they really must send taller people!). I resolved the situation by putting a large car-type hose-clip round it, and it has been fine ever since.

Ironically, the boiler has now been fully "gutted" although, in the final analysis, only one of the items changed was faulty. God knows how long it will be before British Gas makes any money out of my maintenance contract (£12.41/month)!

Still, that’s their problem – they should know more about what they sell.

Since then, and up to the date of writing (26/05/02) all has been well again, and the appreciable gas savings have continued. The boiler has now operated faultlessly for 16 months, with only one routine maintenance visit, to check the composition of its exhaust gases.

VERDICT

If I could award more than one “marks out of five” rating, it would look like this,

Knowledge of showroom staff – 2

Helpfulness of installers – 4

Reliability of hardware – 3 (as time goes by, this will, hopefully get nearer 5 again)

Fuel savings – 5

Usefulness of maintenance contract – 5

SUMMING UP

Anything, which makes better use of the Earth’s finite resources, has to be for everyone’s benefit in the long term.

I did, whoever, get the impression that this was being field-trialled on me, the customer.

Maybe I’ve been unlucky with the initial build quality, and since British Gas saw fit to completely rebuild it, it’s been fine.

Hopefully, their people are a bit more clued-up to dealing with these boilers now!

I certainly wouldn’t cut corners by foregoing the maintenance contract, which followed on from the first year’s warranty, though!
 

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