Old boiler advice - replace or not

coffeehound

I had a megaflo once; t'was a beast: could run a bath in no time!

consequences said:

coffeehound said:

Also there's the chance that fuel prices might go up in coming years as the squeeze is put on fossil fuels. 

Then perhaps its' worth leaving it alone until the point where ASHP and especially GSHP become more cost effective and swap over then.

That would need to be one very well draught-proofed and insulated (walls, windows, roof and floors) 1950s 3-story detached to make a heat pump viable!

Ratechaser I think your decision might come down to this: do you expect your quarter-century-old boiler to last for your coming decade in this home.  If not, and you are going to have to make the investment anyway, then better that you enjoy the benefits now.  Also much better to be in control and have time to plan the work for the summer as tacpot said, and have time for your due dilligence rather than be bounced into it unprepared in the middle of winter and get gouged on price plus any clean-up costs associated with a rusty leak.  You might get a 10-year manufacturer's warranty with the right installer / mx too.  And make the house more saleable too when the time comes.

fred246

My valve had failed. The other thing you can check is your hot and cold water pressure. A pressure gauge is available from Screwfix or Toolstation for about £10. My cold water pressure was a bit high at 6 bar, but the hot from the megaflo exactly 3 bar.

fred246

If the valve fails hopefully it will fail safe and the hot water pressure will be below 3 bar.

Jeepers_Creepers

fred246 said:

The word Megaflo gives it away. Google says that Megaflo can supply 176 litres per minute. A good shower is 20 litres per minute so it should supply 8 showers. If the hot water pressure is at 3 bar it would still be above 2 bar unless the house was taller than 10m which it won't be. All the water goes through the strainer and pressure reducing valve. Clogged up strainer or failed valve likely problem unless inlet pipe is too small or cold water pressure too low.

That's very interesting, Fred.

And if your cold mains supply is 20 lpm, how many showers will it supply?

fred246

That may sound a bit confusing. My flow was poor upstairs. It was sorted by putting a new cartridge in the pressure reducing valve.
Afterwards I bought a water pressure gauge and the cold water was 6 bar and the hot 3 bar. 

Jeepers_Creepers

fred246 said:

That may sound a bit confusing. My flow was poor upstairs. It was sorted by putting a new cartridge in the pressure reducing valve.
Afterwards I bought a water pressure gauge and the cold water was 6 bar and the hot 3 bar. 

Pressure and flow are quite different, although connected (like volts and amps).

Your cold pressure of 6 bar is huge - not many people have that (or would want it - it can cause all sorts of issues). Your hot pressure is 3 bar - that's ideal - almost certainly because a Pressure Reducing Valve is fitted to control this. What this means for you is that you have that massive 'reserve' of 6 bar to keep everything flowing nicely through the 3 bar PRV, regardless of how much water is taken from the other side - you are unlikely to suffer a drop in pressure below 3 bar.

I suspect 'Chaser is starting with a cold mains pressure of around 3 bar, so the more he draws from that, the more it'll almost certainly drop. And the device to suffer most will be the highest/furthest away. 

fred246

The cold water pressure is regulated by the utility company. It has to be over 1 bar which is 10.1974 metres of water. Enough to get cold water to the top of a 3 storey house. 6 bar is too high. I keep planning on contacting them but assume they wouldn't want do anything. I could be wrong?
Anyway 1 to 5 bar is normal for the cold water(most taps and shower valves quote that as their operating range). The hot water goes through a pressure reducing valve with a sieve on the megaflo. So the hot water pressure should be 1-3 bar. Never above 3 bar to protect the Megaflo.
So you need to measure both first. The pressure shouldn't change massively as you use water because the flow rate should be 'mega'. So if you turn two showers on and the pressure goes below 1 bar it implies a restriction. All the water goes through the sieve so a dirty sieve will restrict flow. The PRV and sieve comes as a cartridge. When I changed mine it was well corroded and was a tricky job but fixed the flow. I think you are supposed to have a 'certficate' to work on it so the advice unless you know what you are doing is to get someone in.

Jeepers_Creepers

fred246 said:

The cold water pressure is regulated by the utility company. It has to be over 1 bar which is 10.1974 metres of water. Enough to get cold water to the top of a 3 storey house. 6 bar is too high. I keep planning on contacting them but assume they wouldn't want do anything. I could be wrong?
Anyway 1 to 5 bar is normal for the cold water(most taps and shower valves quote that as their operating range). The hot water goes through a pressure reducing valve with a sieve on the megaflo. So the hot water pressure should be 1-3 bar. Never above 3 bar to protect the Megaflo.
So you need to measure both first. The pressure shouldn't change massively as you use water because the flow rate should be 'mega'. So if you turn two showers on and the pressure goes below 1 bar it implies a restriction. All the water goes through the sieve so a dirty sieve will restrict flow. The PRV and sieve comes as a cartridge. When I changed mine it was well corroded and was a tricky job but fixed the flow. I think you are supposed to have a 'certficate' to work on it so the advice unless you know what you are doing is to get someone in.

If you wanted to balance/protect your system from the excessive 6bar pressure, all you'd need is an additional PRV on the cold side.

Your hot pressure remains at a solid 3bar regardless of how much flow you take from it only because you have a whopping reserve of pressure behind it. Folk who are starting with a static pressure of 3bar will almost certainly notice a drop in flow when more than one outlet is being used simultaneously.

Yes, Chaser should have his Mega serviced and everything checked to see it's working at its best, but if his cold mains is, say, 3bar and 20lpm, then what he is experiencing ain't unusual - it's to be expected.

southcoastrgi

fred246 said:

Google says that Megaflo can supply 176 litres per minute. 

On this occasion google is as truthful as a certain Mr D Trump, there is absolutely no way it can supply that, I would imagine that is the capacity 

Jeepers_Creepers

If you had a cold mains supply delivering 176 lpm, then in theory...