New Gas Boiler

[Spike]

My Boilermate is vented to an F&E tank in the loft. The previous owner used to have the system topped up via the usual live feed through a ball valve. This meant that to clean it out I had to carry several buckets of gungy water down the loft ladder.

For the future I decided to avoid most of this task by adding cooled boiled water to the cleaned tank, sufficient only to cover the pipe to the heat store plus 3mm, adding inhibitor at the same time, leaving the stopcock to the ball valve permanently turned off.

Far easier to empty and clean out, and any leakage (none so far, 15 years later) easily spotted.

[Spike]

Might it not be easier and just as effective to monitor the temperature of the return feed to the boiler, and modulate on that? No remote sensors needed...

[Spike]

My mistake - the ecoFit range has an 'automotive-grade' aluminium heat exchanger, not 'aircraft grade'. Makes it sound even more down-market.

[Max Demian]

You might have storage heaters.

[Theo]

Ah thanks. I thought modulation was reducing the flow temp, but hadn't realised it was also looking at the return temp. Makes sense that it does.

Theo

[Theo]

Once you're on the EV tariff you can use the night rate electricity for whatever you want - they aren't checking it's just used to charge the car. But *you can't get an EV tariff without an EV*. Even if that tariff is attractive for storage heaters, immersions or whatever else.

Theo

[The Natural Philosopher]

Sadly, when you need them the most - very cold outside - heat pumps are probably less than 250% 'efficient' And may well revert to immersion heating as well to boost output.

And of course retrofitting them where a gas boiler has stood means a complete insulation review and larger radiators everywhere.

[The Natural Philosopher]

Bollox. I have never seen then even *claim* over 400% And the proportion of heating that a house uses is massively dependent on thbe number of really cold days.

Right now my oil boiler is off. In winter it runs 24x7.

[The Natural Philosopher]

Yup. The real answer is massive amounts of nuclear power pushing electricity to about 1/4 the price of gas and just use immersion heating. Like the French do. Or underfloor wires.

[The Natural Philosopher]

All boilers do that. That's what the stat on the boiler is for. To shut it off when the water temp in the pipes goes too high.

[The Natural Philosopher]

Flow temp depends on return temp + power input.

[The Natural Philosopher]

That will come down as renewables are phased out

[The Natural Philosopher]

I think you are out by a factor of two.

800% is not possible

[The Natural Philosopher]

One assumes David sells heat pumps and unicorn farts for a living.

[Theo]

That's a safety cutoff, which is something else. This is that, with flow temp X and flow rate Y, we achieve return temp Z. Therefore I know that I'm putting in W watts into the house, and so I need to only generate W watts of heat. And then the weather compensation is tweaking the flow temp (and hence W) up and down based on external conditions.

Most boilers I've had are crude thermostats but, I discover, even a condensing boiler that was fitted in 2009 doesn't (say that it) modulates.

Theo

[The Natural Philosopher]

No, it isn't. It is an adjustable thermostat called 'boiler temperature' or summat

I know because my boiler shuts off even though there is still call for heat on the main stats.

This is that, with flow

[SteveW]

From the manufacturer's information, the boiler can be better controlled and more efficient by monitoring the store temperature and not just the return.

[John Rumm]

It is "controlling" the flow temp, by keeping it to a specified limit. It does this by setting the output power. The output power setting required is a function of the return temp.

So basically as the house comes up to temperature and TRVs start to shut down, the return temp will start to rise. The boiler should spot this, and reduce the output power.

If it reaches a point where it can't keep under the specified max flow temp even when at minimum power, then it will cycle off.

(there is another level to this if you have weather compensation, were the flow temp set point is now also a variable that is inversely proportional to the outside temperature).

[John Rumm]

That is present on pretty much all boilers, but is not modulation as such. Even fixed output boilers will have this, so if the heating load reduces enough the set point on that stat will be exceeded and cycle the boiler off, even if the controls are still calling for heat.

With modulation, the boiler will reduce its output power so as to not exceed the internal thermostat set point. Only if they reach minimum power output, and the flow temp is still over the internal stat set point will they then cycle off. Ideally it will never cycle off on the internal stat, but will reach equilibrium with the rate of heat loss from the house.

[Andy Burns]

An instantaneous 400% is probably meaningless, SFAIUI SCOP means a seasonally adjusted average for the year.

Depending on required flow temperature, there are ASHP models with SCOP over

4.0, with flow temperature of 35 or 40 °C, also GSHP models with SCOP over 4.0 for flow temperature of 45°C, see Vaillant or Kensa specs.