I have had a wee look at BS EN 14825:2022 and it does not seem to mention the defrost cycle. It mentions active mode, thermostat off mode, standby mode, off mode, and the crankcase heater.

It may not be a big problem - I would expect that the fan on the evaporator would keep ice at bay.

Of course, a lot depends upon your location. We get very little fog on the sunny Hampshire coast and only a few freezing days per year.

Any road, how old is, "a bit long in the tooth"?

Any road, how old is, "a bit long in the tooth"?

The main heat exchanger is visibly corroding and spare parts in general are starting to get more difficult to obtain. Not sure exactly how old it is - it came with the house 13 years ago and I suspect was a few years old then - so probably knocking on 20 years old now.

    - Andy.

I'd go for a replacement gas boiler. Why put all of your heat and light sources into one basket? We have a gas cooker for a reason, and that reason is because during the 70's power cuits we had a constant flow of neighbours coming round to boil a kettle. It seems irresponsible to depend exclusively upon the electricity supply for everything in the home, which is why we also retain an electric shower in case the gas boiler develops a fault. It is always a good idea to retain some energy diversity in the home. With a heat pump and electric hot water tank, you are screwed if the black or brown-outs begin as a consequence of all this NOT ZERO nonsense. Heat pumps won't work when the wind doesn't blow, nor the sun shines.

On a recent work trip I done in the more remote parts of Scotland I was told the homes must have a minimum of 2 sources for heat in a dwelling.  This is in case of an outage. 

Why put all of your heat and light sources into one basket?

The gas boiler feeds into a thermal store, which is also fed by a solar thermal panel, wood burner stove and immersion heater - so I have a degree of backup already in place (the gas boiler won't run without electricity anyway). The log burner is on a gravity circuit and will boil a kettle directly anyway - so should be reasonably power cut tolerant. Torches and if needs be candles for light.

   - Andy.

whjohnson said:

during the 70's power cuits we had a constant flow of neighbours coming round to boil a kettle

I recall a neighbour bringing round the Sunday roast.

whjohnson said:

It is always a good idea to retain some energy diversity in the home.

A very good point.

If you have a hot water tank, at least you can cope for a while.

I see what you mean. Ours are more like 40 years old, but they are floor-standing cast iron ones so they should last forever. Whether the electrics will do so is another matter.

I have had a wee look at BS EN 14825:2022 and it does not seem to mention the defrost cycle. It mentions active mode, thermostat off mode, standby mode, off mode, and the crankcase heater.

Interesting. I've read (I think in a MCS document) that the figures are normally based on "SEPEMO ‘boundaries" - which seem to include the electricity used by all the auxiliary parts usually inside the box (pumps, auxiliary heaters and so on) - so I was hoping that any electrical defrost heater would be included in that, likewise a reverse refrigerant system would reduce the cumulative heat output, so again should be counted. By big worry is how often the defrost cycle would be needed in reality, compared with lab conditions (not that I'd expect manufacturers to choose conditions that gave the most favourable result or anything).

It may not be a big problem - I would expect that the fan on the evaporator would keep ice at bay.

I'm not sure how much heat the fan would produce (low noise, low energy seems to be the order of the day), plus some of the ones I've been looking at seem to have the fan at the back/outlet side. I might suspect that things could well be arranged to reduce the problem (e.g. the front layer of the evaporator being at a slightly higher (above zero) temperature than the main part (but mostly still below air temperature), encouraging condensation to form there where it can drip away without freezing and so reduce the ice load on the main (cooler) part of the evaporator. 

Of course, a lot depends upon your location. We get very little fog on the sunny Hampshire coast and only a few freezing days per year.

Unfortunately, I'm in the lea of the Pennines where cold and damp seem to be the norm in the bottom half of the year. Still there'll be  solution, I just have to find it!

   - Andy.

I have had a wee look at BS EN 14825:2022 and it does not seem to mention the defrost cycle. It mentions active mode, thermostat off mode, standby mode, off mode, and the crankcase heater.

Interesting. I've read (I think in a MCS document) that the figures are normally based on "SEPEMO ‘boundaries" - which seem to include the electricity used by all the auxiliary parts usually inside the box (pumps, auxiliary heaters and so on) - so I was hoping that any electrical defrost heater would be included in that, likewise a reverse refrigerant system would reduce the cumulative heat output, so again should be counted. By big worry is how often the defrost cycle would be needed in reality, compared with lab conditions (not that I'd expect manufacturers to choose conditions that gave the most favourable result or anything).

It may not be a big problem - I would expect that the fan on the evaporator would keep ice at bay.

I'm not sure how much heat the fan would produce (low noise, low energy seems to be the order of the day), plus some of the ones I've been looking at seem to have the fan at the back/outlet side. I might suspect that things could well be arranged to reduce the problem (e.g. the front layer of the evaporator being at a slightly higher (above zero) temperature than the main part (but mostly still below air temperature), encouraging condensation to form there where it can drip away without freezing and so reduce the ice load on the main (cooler) part of the evaporator. 

Of course, a lot depends upon your location. We get very little fog on the sunny Hampshire coast and only a few freezing days per year.

Unfortunately, I'm in the lea of the Pennines where cold and damp seem to be the norm in the bottom half of the year. Still there'll be  solution, I just have to find it!

   - Andy.