Back boiler. Stiff nipple screw?!

[FrancisJK]

I know, I know.

The screw in the pressure test nipple is stuck. It won't turn.

Maybe it hasn't moved since it was commissioned.

How do I loosen it?

Francis

[FrancisJK]

Baxi Bermuda 552.

The diagram in the manual is difficult to read. The arrow points to a pressure test nipple for setting burner pressure. There is a metal screw cap covering govenor. The setting on govenor is a plastic? slotted knob. No scale on knob to indicate pressure. Is it dependand on imput pressure?

Francis.

PS

Was up to 74 deg C before I shut down. Too hot in house.

[Andy]

Just out of interest what sort of back boiler is it? I assume when you say the test point you mean the burner pressure test point not the inlet pressure.

Andy

[Set Square]

The governor controls *output* pressure - and is sensitive to *flow rate* rather than input pressure, which is why you have to set it with the boiler running at full whack.

The adjustment screw bears on the end of a light spring, and probably requires many turns to make any appreciable difference to the pressure - so there are no pressure markings, the only way being to attach a manometer to the test point.

Have you managed to get the screw out yet? If not, is it because you are unable to supply enough torque to shift it, or because the slot is damaged and the screwdriver is slipping off? If the slot is ok, use a screwdriver bit in a small socket set in order to be able to exert a bit more torque.

If it's totally impossible to get the screw out of the test nipple, there

*is* an alternative way of setting the pressure. The boiler manual should have a table showing input power (BThU/Hr or kW) for each of several pressure settings. From these, you can calculate gas flow rate ** - including how long it should take the little test pointer on your gas meter to revolve through 360 degrees. You can time (with a stopwatch) how long it *actually* takes with the boiler running continuously, and adjust the pressure to get the right flow rate. It's a bit fiddly and obviously takes a lot longer than using a manometer - but it *can* be done. [Even if you use a manometer, it's a good idea also to measure the flow rate, as a sanity check].

** The relationship between gas volume and energy should be explained in the calculation on your gas bill - and you have, in effect, to run this calculation backwards.

[FrancisJK]

Thanks for that. The slot seems ok. It's getting the torque on it that is the problem.

Don't want to damage the controls, or me.

Will report back tomorrow.

Francis

[Ian Stirling]

It's really hard to damage a screw by pressing too hard on it. It's easy to damage the slot if you'r not pressing hard enough, and the screwdriver cams out. Find a screwdriver of the right size, and ensure it's not loose in the slot before attempting.

[FrancisJK]

And me?!

Already damaged me yesterday, trying to tighten a 1" compression fitting.

Will look for an exact size screwdriver in the cool light of day tomorrow.

And give it a bash so to speak.

Otherwise it's out with me stopwatch and calculator AND umbrella and use Set Square's idea.

Francis

[FrancisJK]

Woo Hoo!

It's now a slack nipple screw, with no injuries to the operator.

I have a big bruise and sore from the compression fitting.

The instructions say slacken, so I don't take it out?

Now, how do I get my manometer rubber onto the nipple?

Francis

[Set Square]

I've always taken mine out (so to speak!). It will be easier to fit the manometer without the screw in place. I think that the nipple is on the burner side of the gas valve - so you won't get any gas leakage if you fit and remove the manometer with the boiler turned off.

Make sure that the boiler has been running for few minutes to warm up and establish steady-state conditions before adjusting the pressure.

[FrancisJK]

Manometer connected.

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

[Ed Sirett]

If the flames look good, the pressure is within the accpetable range (most back boilers are range rated) and the boiler does its job. I advise you to leave things where they are.

[FrancisJK]

Switching of system now to install new trv.

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 heavy mofu). My burner, controls etc.

Also got an overheat thermostat kit and went sealed.

Unless his heat exchanger is full of gunk, (Ah.. never thought of flushing it out before putting it in)I can't see what other variables are effecting the temp.

Max flow seems to be 70 deg C

Francis

[Set Square]

Is 70 degC the most you can achieve with the boiler stat turned up to max, and the room stat turned up keep to ensure that the system keeps running? If so, you probably won't even achieve that in the winter, when much more heat is flowing out of the house. Have you got over-sized radiators which can provide sufficient heat even with a low flow temperature? If not, you might feel a little cool! [I would expect a flow temperature of around 80-82, and a return temp of about 70, so that each rad runs at a mean temp of around

75-76. If you're running 10 deg cooler than this, the output of your rads will be reduced by getting on for 25%].

As an aside, are you sure that a Baxi Bermuda is ok in a sealed system - I'd be surprised if it was designed with sealed systems in mind?

[FrancisJK]

Have install my new TRV, refilling.

Manual says can be used sealed if overheat thermostat used.

Have BAXI kit installed.

Mislayed my temp figures from last year but I think higher flow than 70 Deg C

Francis

[FrancisJK]

Filled and heating up.

The plan is to get a superduper new boiler.

It may be sooner rather than later.

Francis

[Ed Sirett]

Usually the boiler thermostats on these boiler fail high rather than low. Because of : wear in the machanism. leakage of fluid from the sensor bulb. misplacement of the sensor.

If the boiler is really on half power and you have mor than about 6 rads then 10kW is probably too low.

Incidentally mix'n'match boiler maintenance is not the way to go. 8-(

[FrancisJK]

SNIP

Bermuda 552.

All I needed was the combustion box. Mine had corroded around where the three exit holes were for the flow and return pipes.

Used combustion box and heat exchanger. Was going to buy replacement parts but just for those two would have cost ?600

When you say fail high, do you mean stuck on high or boiler won't heat beyond a certain temp.

We have 7 rads, two of those are doubles.

Francis

[Set Square]

No! "Fail high" means that the thermostat fails to detect that the required temperature has been reached - with the result that the boiler fires continuously - and over-heats unless protected by some other device.

[FrancisJK]

OK

No that not happening. Boiler is cycling and Overheat thermostat has never tripped.

Got up to 150 deg C yesterday but reckon battery in test meter needs changing!!!

See new thread

"Goin 4 D Big 1 Hughie" - Boiler

Francis

[FrancisJK]

Thanks, Ed.

Leaving set at 11 mbar. Flames nice and blue.

Pity Pandora didn't listen to you.

Francis