Combi Boiler Pressure Drop

[Phil Richards]

First of all I know very little about boilers, so please be patient!

Having got a decorator to remove and drain out a radiator so as he could paint behind it, on reconnecting and turning the hot water inflow back on, we noticed the pressure on the system drop from about 1.2 to almost zero. This didn't surprise him as basically we took out a fair proportion of the water in the system (total of 4 radiators in our flat).

Problem is now we can't see away of replenishing the water back in. Examining the pipe work underneath the boiler, the chap helping me saw that the two pipes to the RHS of the photo below should be connected by the flexible silver pipe just hanging over it!

At that point he gave up and said to get expert advice! Fortunately we have a fixed service contract with British Gas who only 7 months ago carried out a service check and presumably this didn't appear out of the norm. They are due out Monday morning.

On speaking to someone else, from my descriptions he reckoned the system is sealed. There is no water tank in the loft, all water comes in from the mains and he reckoned sometimes once a boiler like this is set up and the system filled up with water, often the water supply is disconnected.

So my questions are:

1. The boiler seems to run OK on a much lower pressure, with the radiators at their normal heat. The only difference is you can hear air in the system. Is it safe to keep the system running this until the engineer comes out Monday, especially as the current cold weather is forecast for the weekend?

1. How on earth is a system supposed to be refilled easily when radiators are drained out? Or is there another way of allowing mains water into the system.

2. How easily would it be for the engineer to get the pressure back? I only hope that especially as British Gas have already examined the system (on two occasions, once after it developed a fault, the other a service check) they will not say I've tampered it or it is a design fault.

Many thanks.

[Owain]

By connecting the flexible silver pipe between the cold water main and the radiator circuit, and turning the taps on until the pressure gauge goe up to .

Are you saying there are now no screw-on connection points for the flexible pipe?

Very easy assuming there are screw-on connection points for the flexible pipe. I don't know what British Gas will say - be prepared for them to tell you you need a new boiler.

Owain

[Phil Richards]

Perhaps not too clear from the photo I took, there are screw on connections on both pipes on the RHS. I can see now how easy the job will probably be. What I don't understand is why they effectively got sealed off presumably after the boiler and radiator system were installed making it difficult to top it up after, say what I did, by draining out one radiator.

Well I hope not.....

[Richard Faulkner]

I understand that it is correct for the silver tube to be removed but, usually, you can just screw it back on and open the taps to fill the system.

Are the pipes capped and sealed? Or will the caps pop off to allow you to screw the pipe on?

[John Rumm]

All the information and some background as to how your system works can be found here:

So my questions are:

Depends on how low the pressure is... some boilers will refuse to fire without enough in the system. Sounds like yours is running OK though.

Via the "filling loop" (i.e. that hose of yours). There are two connection points: one is a tap - this is on the cold main supply. The other is a non return valve on the heating system. This lets water into the heating system but not out.

The only slight extra wrinkle with your setup is it looks like someone has screwed caps onto the filling loop connection points. This is no bad idea since it keeps dust and other crud out of the ends of the valves etc. You should find the caps unscrew easily by hand. No water should come out when you take the caps off.

It is "correct" to disconnect the filling loop once the system is filled. (basically it is another safeguard that prevents any possibility of contaminanted dirty water out of your heating system getting back into the drinkable mains supply)

Very easy. Connect up the loop and open the tap. Watch the pressure guage and turn off when at the right pressure. Bleed any air from the radiators. Top up the pressure if neccessary. Repeat until there is no more air to bleed. See the FAQ for a full description.

No, your system looks fine. Topping up the pressure is one of those tasks that you will usually only need to do should you remove rads etc.

[Andrew Gabriel]

The filling loop must be disconnected when not being used. This is to prevent any remote chance of the radiator water getting back into the fresh water supply. I can't see clearly in the photo, but the supply end should have a tap and the heating end should have a one-way valve to prevent water coming back out.

[Phil Richards]

Many thanks to John, Owain & Richard for all their help. I must say out of the many newsgroups I read this seems to be one of the friendliest & most helpful!

[<me9]

It must be one of a few that comply. Most seem to leave the filling hose connected. There appears to be a tap on the right of the photo , over which the hose iis draped. It looks as if the filling point and supply are capped with brass compression stop ends.

[Ed Sirett]

More likely 1/2" BSP brass caps. This year a boiler I had installed was inspected and was told that I had left the filling loop connected. I was sent a letter telling me to go and disconnect it.

I disagree that the best practice is to disconnect the loop, but that's what our lords and masters require, eh. A small quantity of water dribbles out of the loop after disconnection (OK so you can use a cloth to catch it). Also a small amount of air is introduced into the system when it's reused. Also dust caps are not supplied with most filling loops so these have either to be supplied or the possibility of 'foreign' matter getting in has to be endured.

[Andrew Gabriel]

Yes. I connect up the supply end first and very loosely connect the heating end, turn on the water so it blows most of the air out of the loose connection, before tightening it up to force the water through to the heating system.

or of young enquiring minds thinking "what happens if I turn this knob?" ;-)

Mine's in a rather shallow cupboard, and the door won't stay shut if the filling loop is left connected anyway.

[--s-p-o-n-i-x--]

From the photo, it looks like they are indeed sealed with brass, threaded caps.

[The Natural Philosopher]

Because you are NOT supposed to leave the flexi pipe permamantly connected, although everyone actually does.