Radiator replacement. Now heating won't work. Help!

manatoo

Hi

I had to change a radiator today. I isolated and removed the old one and reconnected the new one no problem. Upon fitting the new one and hooking the pipes back up I noticed very low pressure in the radiators when bleeding them from the bottom floor up. Turning the heating on resulted in a lot of banging and an overheat warning and shutdown of the boiler.

Am I right in thinking the boiler has no water going through it either due to low pressure or because there's an airlock?

The boiler doesn't have its own pressure gauge. It's over 20 years old but was working fine up until today, including with the radiator removed.

If it was a matter of pressure I would have thought i could use the filling loop to push pressure back into the boiler but having stripped the house to pieces there doesn't seem to be a filling loop anywhere in the house.

All out of ideas. Can anyone help??

Thanks

listermint

Have you bled all the radiators again. ? I usually do mine about 4 times if I've removed a radiator

manatoo

listermint wrote: »

Have you bled all the radiators again. ? I usually do mine about 4 times if I've removed a radiator

I've gone around them all to make sure water is coming out the bleed nipples. I don't think there's any more bleeding to be done?

Do you have to repressurise your system after taking rads off?

manatoo

Hi all

So messing around with bleeding the radiators has allowed me to get the radiators working again and the boiler has settled down but there are two radiators in the converted attic which I can't get to heat fully to the top.

Bleeding the radiators doesn't have any effect, there's no pressure in them. What's notable is that they're on the same level as the tank which is in the crawl space under the rafters in the non-converted part of the attic, if that makes sense. To the best of my knowledge it's a gravity system so how could the radiators possibly fill up to a level as high as the tank? Is there some trick to get it it?

Thanks!

John.G

As long as the level of water in the header tank is higher than the rad(s) top then water should flow from the vents, a lot of older systems had the feed&expansion tank mounted above the cold water storage tank to give that extra head but is now frowned on as the CWST can be contaminated in the event of a holed cylinder coil.
Your rads are probably circulating with a partial vacuum, mine (attic) does, I have occasionally filled the header tank to its overflow and then with system shut down, vented the rad from either end, it eventually does heat up fully to the top.

manatoo

John.G wrote: »

As long as the level of water in the header tank is higher than the rad(s) top then water should flow from the vents, a lot of older systems had the feed&expansion tank mounted above the cold water storage tank to give that extra head but is now frowned on as the CWST can be contaminated in the event of a holed cylinder coil.
Your rads are probably circulating with a partial vacuum, mine (attic) does, I have occasionally filled the header tank to its overflow and then with system shut down, vented the rad from either end, it eventually does heat up fully to the top.

Thanks John. Are you saying it's ok for there to be air in the attic rads and for them not to be full to the top?

Also, I'm not clear on the setup because although there are two tanks in my attic they're identical in size and level and appear to just be connected together through a small length of pipe at the lowest point between the two tanks. Are you saying I should open the vents on the attic radiators and fill the two tanks up higher to see if additional pressure will fill the rads?

John.G

I'm not quite saying that its OK to have air in the rads, I,m saying that water does come from my vents with the circ pump off but with pump on no water from vents which means that it is running under a slight vacuum, not desirable but hasn't caused any problems in my 40 year old system and the attic rad does heat up fully.
If water comes from your rad vents with circ pump off then probably no need to raise the level. Its surprising that the rads are fed from the CWST(s), I have seen this but with a non return valve on the cold feed to the system and a expansion vessel installed, the pressure will then rise a little when the system heats up.
Is the water level higher than the top of the rads?.

manatoo

John.G wrote: »

I'm not quite saying that its OK to have air in the rads, I,m saying that water does come from my vents with the circ pump off but with pump on no water from vents which means that it is running under a slight vacuum, not desirable but hasn't caused any problems in my 40 year old system and the attic rad does heat up fully.
If water comes from your rad vents with circ pump off then probably no need to raise the level. Its surprising that the rads are fed from the CWST(s), I have seen this but with a non return valve on the cold feed to the system and a expansion vessel installed, the pressure will then rise a little when the system heats up.
Is the water level higher than the top of the rads?.

Just checked there and no, both tanks are not as high as the highest point on the rads. This is what I can't figure out. How could the rads ever be full if they're higher than the f+e tanks?

There is a smallish red expansion tank in the hotpress a floor below but I understood that was on the hot water circuit and not the heating.

John.G

Are there one or more 3/4 ins vents bent over the CWSTs, if only one then tis is from your vented HW Cylinder and would point to a filling loop somewhere with a pressure gauge for the heating system. If the heating system is gravity then there should be two vents. It should be easy to see where the Exp vessel is if connected to the heating system, maybe into the cylinder coil return?

manatoo

John.G wrote: »

Are there one or more 3/4 ins vents bent over the CWSTs, if only one then tis is from your vented HW Cylinder and would point to a filling loop somewhere with a pressure gauge for the heating system. If the heating system is gravity then there should be two vents. It should be easy to see where the Exp vessel is if connected to the heating system, maybe into the cylinder coil return?

There is indeed one copper pipe that arches up over one end of one of the tanks.

The exp vessel is on a dead end pipe just above the HW cylinder, ie- not on the side of a pipe in a T-junction type arrangement. Would that mean it's part of the heating system? There's no pressure gauge there though. The only pressure gauges I can find are one on an outlet vent line in the wall above the boiler which I think is for over-pressure release and there's a second one below the kitchen floor somewhere near where the mains comes into the house. There's no pressure gauge on the boiler itself and I've never been able to find the braided pipe that would indicate a filling loop. That's why I thought it wasn't a pressurised system

John.G

If a gravity system then the vent is often a continuation of the HW cylinder heating coil flow (top) inlet at the side of the cylinder, have a look at this and see if the 3/4 ins pipe does continue on up and terminate in the vent.

If the expansion vessel is connected directly to the top of the cylinder then you have a unvented (pressurised) hot water system and you should hear a pump starting/stopping each time you open a hot water tap (and probably start/stop if a cold water tap upstairs is opened). Not sure what you mean by a dead end pipe except its connected to the cylinder as I just said.

If the boiler PRV has a pressure gauge then it must be connected in before the PRV and should read a minimum of 0.35/0.5 bar (if a gravity system), it wouldn't make any sense if connected after the PRV as this pipe is then just the waste pipe from the PRV and is "never" pressurised.

There are plenty of systems around without braided filling hoses but all will have at least one isolation valve and the pressure gauge may be part of a pressure reducing valve (also called a PRV) from the mains (see pic). Your system might look something like either of the two depending on gravity system or pressurised system.
Can you post a few photos of the piping and pressure gauges and their displayed pressures.

manatoo

If I know the kind of pump you're talking about, it's in all modern apartment blocks right? Definitely does not have that kind of pump. I've a friend with a new semi detached house which has that same pump in so I can say with certainty I don't have that. My house is built in the 1950s and the boiler has an installation date in 1994 on it so the heating system is at least that old if that tells you anything.

I've attached pictures as you suggested. Unfortunately the ones under the kitchen floor are poor quality because it's dark and the pipes wind all over the place from there. The pressure gauge under the kitchen floor always reads around 0.4 and the one behind the boiler is always at zero unless the heating is on when it rises very slightly.

Hopefully these are of some use.

manatoo

Further pics - there's a limit of 6 per posting

manatoo

Sorry, should just add that the red expansion vessel you can see under the kitchen floor isn't connected to anything. I gather at some point in the past it broke and a plumber disconnected it and rather than cut the floor joists to get it out he left it there. It's full of water so I'd imagine it just failed.

John.G

OK. its becoming clearer now, I think your plumber just installed a new Exp vessel upstairs and you have a sealed heating system.
Just carry out the instructions on the attachment and you might be back in business.

manatoo

John.G wrote: »

OK. its becoming clearer now, I think your plumber just installed a new Exp vessel upstairs and you have a sealed heating system.
Just carry out the instructions on the attachment and you might be back in business.

What pressure am I looking to get to on the PRV gauge at the boiler?

John.G

If system is cold/cool try 1.2/1.3 bar then see what final pressure is when system is fully hot, if system is hot just now suggest 2 bar, ideally you should have 1.3/1.5 bar at the boiler when cold, this should mean a pressure of 1.8/2.3 bar when hot but doesn't matter as long as it isnt> say 2.7 bar when hot, final setting should be done with a cold system.

manatoo

John.G wrote: »

If system is cold/cool try 1.2/1.3 bar then see what final pressure is when system is fully hot, if system is hot just now suggest 2 bar, ideally you should have 1.3/1.5 bar at the boiler when cold, this should mean a pressure of 1.8/2.3 bar when hot but doesn't matter as long as it isnt> say 2.7 bar when hot, final setting should be done with a cold system.

Ok twisting that black knob did nothing at all. In fact it was already fully open. Gauge on that connection (under kitchen floor) is showing 0.6.
Could there be anywhere else that it would be shut off?

John.G

Check for isolating valve where shown in attachment, then open black knob and turn the adjusting screw clockwise until pressure rises (although this screw does look screwed down well), there is also another (red) gate valve to the far right, may also be worth checking even though I think the mains comes in to the left of this, also give the PRV a few whacks of a spanner but do not hit the pressure gauge, PRV/piping may be partially blocked.

manatoo

John.G wrote: »

Check for isolating valve where shown in attachment, then open black knob and turn the adjusting screw clockwise until pressure rises (although this screw does look screwed down well), there is also another (red) gate valve to the far right, may also be worth checking even though I think the mains comes in to the left of this, also give the PRV a few whacks of a spanner but do not hit the pressure gauge, PRV/piping may be partially blocked.

Screwing the adjuster worked. Pressure is now at 1 bar under the kitchen floor and the PRV gauge is now at 0.5 bar. Pictures attached. I've closed the black knob as you said.

System is cold. Should I try firing it up or should I keep adding water to get pressure at the PRV higher?

John.G

That's good news!!....I would get the boiler pressure up to 1.0 bar now (cold), fire up and see what the final pressure is with all systems hot.

manatoo

System hot. Pressures are as per the pics on the two gauges and the attic rads are piping hot right to the top after two bleeds and

You sir are a gentleman and an engineer. I really appreciate the help.

I'm assuming you're a plumber? Are you based in Dublin?

Just need to tackle boiler replacement, bathroom replacement, solar installation and underfloor for the ground floor next. You send the instructions and I'll do as told ok?

manatoo

Correct second pic above

John.G

No, not a plumber or based in Dublin but was a engineer for ~ 45 years.

manatoo

John.G wrote: »

No, not a plumber or based in Dublin but was a engineer for ~ 45 years.

Tip of my cap to your skills sir. What I'd give to have your knowledge.