"We have Lift-off!" Sealed CH System

If it lifts off, you've set the pressure too high. :)

Yes, Normal.

The rise in pressure is normal and about right.

The expansion vessel sizing is near the limit.

For a 3bar relief valve (normal one) and an initial charge pressure of 0.5 bar in the vessel, 75 litres of water would need 6.3 litres of vessel and 100 litres 8.3.

So if you are much over 86 litres, then you may need a larger or additional vessel. This will become apparent if the pressure climbs much over 2 - 2.5 bar

.andy

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Reminds me of my father:

"The only time the family went out together was when the boiler blew up!"

Francis

Now have a an air pressure gauge. Air in vessel 0.5 bar. Static head of system 4.7 metres.

Pressured system when cold to 0.7 bar.

When hot, pressure is about 1.1 bar.

Still some weeping on some compression joints.

Tested the system for about an hour tonight.

Will report later.

Francis

Just realized that the 86 litres would include header tank and feed pipe and safety vent. Now have to calculate that and subtract from 86.

Francis

A sealed system does not have a header tank.

No, the 86 litres was from the open vented before I converted. As we drained we measured (in buckets), but that would have included header tank etc which is no longer in system.

Francis

That's only going to be another (less than) 10 litres, but if you think that 86 was the max then you should be OK.

If not, it will soon become apparent

You could try winding up the temperature and see if you hit the safety valve limit.

I would guess probably not now that the header is out of the equation.....

.andy

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Didn't get around to DIY today.

Will try heating to max and see what happens.

francis

Had to rejiggig some pipe and have most compression leaks tightened.

I can't remember how hot the flow was on the vented set-up. So far flow up to 70 deg C

FrancisJK

Normally the design temperatures for a conventional (i.e. non-condensing) boiler are 82 degrees flow and 70 return. Generally radiators are sized to work with this and to be able to maintain room temperatures at -1 or -3 degrees outside.

It is desirable to run the boiler flow at this kind of temperature anyway because if the return approaches 54 degrees you are getting to the point where there will be condensing of the flue gases inside the boiler. In one not designed to take it like this, that would be bad news as it would lead to rapid corrosion.

It's possible on an older boiler that the thermostat is on its way out of course.

I would measure the return temperature and see what it's like when everything is up to temperature. If it's below 60 then something does need to be done.

.andy

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Thanks Andy,

Your figures sound like what I had on the vented set up.

History.

Last Summer I got around to upgrading system.

Back boiler, fully pumped, open vent. No controls other than timer.

Redesigned using U-values and all that good stuff on Rocky Prescott's site.

Flushed system.

Some new rads, old ones taken outside flushed out

New programmer, thermostats, zone valves.

Annual boiler service: "Signs of corrosion, could go tomorrow or last a few more years"

Saving for a new boiler.

In mean time, neighbour threw out old boiler, exact model. I salvaged parts from it, got some newer parts.

Using neighbours combustion box and heat exchanger (a have mofu). My burner, controls etc.

Also got an overheat thermostat kit and went sealed.

Unless his heat exchanger is full of gunk, I can't see what other variables are effecting the temp.

Gonna switch on now and check temps.

Francis

Up to 74 deg C now

Francis

Got me stiff nipple screw unstuck so will now be able to check burner pressure.

Also got cleaner and will run system to clean out any gunk.

Francis

Manometer connected to check burner pressure.

Little over 10 mbar, which according to manual is about half of pressure available, Output 12.8 kW 43,000Btu/h

Max setting available 17 mbar, 16.1kW 55,000 Btu/h

Francis

I don't know whether the regulations in Ireland follow the UK, Francis (I know they do in some aspects of electricity for example), but there is a spec. for the max allowable pressure drop between the meter and the input of any appliance when running of no more than 1mB.

I would suggest that you check the incoming pressure at the boiler as well (i.e. on the input side of the regulator) to make sure that this is not being violated if you decide to wind up the regulator setting.

.andy

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They usually do, although prices don't.

I have found it quicker and cheaper to get stuff shipped from the UK to here, and that includes delivery.

Might be going over for the boiler "it's hand luggage Mr Ryanair"

Francis

"FrancisJK" wrote | I have found it quicker and cheaper to get stuff shipped from | the UK to here, and that includes delivery. | Might be going over for the boiler "it's hand luggage Mr Ryanair"

At their fares vs excess baggage charges, be cheaper to take a couple of rugby teams over for the day, dismantle the boiler into 30 pieces and bring it back one piece each.

Or put little wheels on it and come back on the ferry as a foot passenger, tell them it's a gas-powered chair for the disabled.

Owain