O/T Free beer/donation to REMF/eternal gratitude extended to CH plumber...

....if they can help with the following issue.

I have a big problem with my CH system losing pressure and gaining air, and it's driving me nuts and, tbh, the plumber I'm using is now looking to me for suggestions as to how to fix it and I'm out of Google-based solutions.

Background:

I have a sealed CH system, but the HW is open vent (small F&E tank in the loft). The boiler is a system (not combi) Camray 5 50/70 (50,000 - 70,000 BTU) wall-hung, internal, oil-fired boiler - about 10 years old - serviced every year. I have a HW tank and a single pump (new - see below), two motorised valves (which both seem to work ok) and a (new - see below) expansion vessel in the airing cupboard on the first floor. I now have 14 rads in total (with two having been very recently fitted).

I've recently bought this property and had two new rads fitted - one on the first floor and roughly the same height as the pump etc, and one in a loft conversion - clearly higher. The flow pipe has been tee'd off the main CH flow just downstream of the CH motorised valve, and the return tees into the main collecting returning pipe. I've now had a non-return valve fitted on the new return section since the pipework was getting hot when just the HW was on. The pipework for both these new rads goes up from the airing cupboard, around the eaves and drops down the wall to the new rad on the first floor landing and continues round (in parallel, not series) to the rad in the loft conversion. A new beefier Grundfos pump was fitted to get the water up a storey and to cope with two additonal rads.

Problem:

I continually get air in the system - as evidenced by massive gurgling in the pipework down to the new landing rad (as well as elsewhere); and lose loads of pressure 1.4bar cold pressure down to 0.8bar cold pressure in 24 hours - but then, weirdly, it seems to tail off, never getting lower than 0.7 bar.

Attempted fixes:

1 Look for leaks inside - none; though some of the pipework runs under a concrete floor. Pipes and floor laid 9 years ago. (Arrrggghhh...don't tell me)
2 Look for leaks in boiler - none apparent, and there's no overflow pipe for expanded water coming from the boiler
3 Look for leak from overflow pipe from pressure relief valve on top of expansion vessel. Ah ha! It leaks...and, on checking the pressure the hot pressure is 2.8 bar. Bugger me, that seems like a massive increase in pressure from the cold pressure of 1.4 bar! So - google search. Google says that the difference in pressure between cold and hot s/be 0.3-0.6 bar (not 1.4 bar). main cause for fault? Knackered expansion vessel. OK - let's change the expansion vessel. OK - what size Expansion vessel should I get? Google says s/be measured by volume of water in the system (wtf - how do I know?!) OR, rough rule of thumb, = 1.5 -2.0 litres per rad, or 1 litre per KW of boiler. OK! 14 rads = 21-28 litres; boiler = 21 KW max. Google also says you can't have one that's too big, but you can have one that's too small. So... let's get a 24 litre expansion vessel, with attached new pressure relief valve, in case the existing prv is buggered having been opened and closed several times. Done, and fitted. Air side pressure is left at manufacturer's factory setting of 1.5 bar. System pressurised to 1.4 bar cold. Run system last night - very quiet, no problems - hot pressure maxes at 1.9 bar. Ah ha! I've fixed it! Nope - this morning, the cold pressure is back down to 0.75 bar. Aaaargh.

Questions:

1 WTF is going on?
2 Specifically, I can think of only two possible solutions: a) the hot water loop and CH loop in the HW cylinder is breached and water is flowing from CH to HW under pressure. My plumber, in whom I am losing trust, says it can't be that since I'd smell the inhibitor which he put in only 3 weeks ago from the CH system in the hot water when I run a HW tap. b) I have a massive leak in the pipework embedded in the concrete floor.

Are there other possible causes for these symptoms?
Is it true that I'd def smell the inhibitor in the HW flow if the loops have been breached?
Is the only way to tell if the under-concrete pipes are leaking to get a thermal camera? If they are leaking - is there any way to solve the problem other than digging the floor up?
How come the cold water pressure stabilises at about 0.7 bar - if there's a leak - why isn't it diminishing to zero??

Thanks for reading - as I say - a beer/donation/eternal gratitude extended to any plumber who fancies replying.... I'm going kin nuts now.

Do you have mains to kitchen only, or too other cold draw off points/bathroom ?
If you had crossover/cross contamination then the HW and any downservice cold water would smell as inhibitor would be in it and 1.4bar top up is (likely..) higher than any gravity supplies.
And if it was the mains cold to kitchen crossover, then mains would 'fill' up the pressure in the CH.. Overall, I think it's very unlikely this is it.
0.7 bar of pressure is 7m of head - what is 7m high up water wise.. a radiator?

(I dont know these boilers, but sounds like you've covered all the obvious points, hope others can help)

Have you tried turning it off and on again?

I have no specialist knowledge whatsoever, but we had something similar and it was a corroded pipe embedded in the (concrete) floor. On uncovering it plumber said it hadn't been encased properly, allowing the concrete to corrode the pipe - house is late 70s though and this was maybe 8-10 years ago, so pipe had been there for about 30 years

I thought Chris Houghton was a lift engineer before he got into football not a plumber, don't think he can help you.

Rowdey said:

Do you have mains to kitchen only, or too other cold draw off points/bathroom ?
If you had crossover/cross contamination then the HW and any downservice cold water would smell as inhibitor would be in it and 1.4bar top up is (likely..) higher than any gravity supplies.
And if it was the mains cold to kitchen crossover, then mains would 'fill' up the pressure in the CH.. Overall, I think it's very unlikely this is it.
0.7 bar of pressure is 7m of head - what is 7m high up water wise.. a radiator?

(I dont know these boilers, but sounds like you've covered all the obvious points, hope others can help)

Click to expand...

Cheers.

There is mains cold to kitchen and also to a ground floor (f)utility room as well as to two outside taps. Bathroom is on the first floor and cold is tank fed. Yes, I guess there is a rad at 7m from ground level - but the pressure gauge itself is at 5m - wouldn't the differential only be 0.2 bar?? Also, if the fault is a leak in the downstairs under concrete pipework, wouldn't the water continue to drain out the system until (eventually) it was completely empty?

EDIT: Why did you ask whether I have more than one cold mains draw-off point? Is it significant that indeed I do?

How old is the original system? I.e the rads not just the boiler.

Was the boiler and main rads fitted new 10 years ago.

A possibility is if there was and old boiler and radiator system that was open vented originally which had a sludge/air problem. Then your new 10 year old boiler ( Sealed System ) fitted on to the old system with a sludge problem. Which can causes gassing in the system which can escape from auto Air vents if they are fitted, dropping the pressure.

Do you have to bleed rads at all? as you shouldn't need to on a sealed system, this could indicate sludge problems.

Just a thought as you mentioned a new more powerful pump.



The cylinder coil is a possibility, I wouldn't go with the smelling the inhibitor as 1 liter of inhibitor in 100 liters of water transferring into a 140 litre approx. cylinder of water will be so diluted I doubt you notice it. Especially when a bath may use a 100 liters of water a time.

The cylider change wouldn't be cheap so best to be sure before jumping in.


Do you have an Electric Immersion heater to heat the water?

If yes you could drain the heating system and fit 2 isolation Valves in the flow and return to the cylinder refill and temporally just use the boiler for the central heating and the electric immersion for hot water.

This way you could prove one way or the other if the cylinder ( Its coil ) is the problem. Then just open the valves if its ok and switch back to using the boiler to heat it.

My hunch is it's not the cylinder as they rarely fail this way ( does happen but not often )
Good luck

[MENTION=25123]SIMMO SAYS[/MENTION] is your man here, that is if he's finished destroying Lamie's Bathroom.

jon12345 said:

How old is the original system? I.e the rads not just the boiler.

Was the boiler and main rads fitted new 10 years ago.

A possibility is if there was and old boiler and radiator system that was open vented originally which had a sludge/air problem. Then your new 10 year old boiler ( Sealed System ) fitted on to the old system with a sludge problem. Which can causes gassing in the system which can escape from auto Air vents if they are fitted, dropping the pressure.

Do you have to bleed rads at all? as you shouldn't need to on a sealed system, this could indicate sludge problems.

Just a thought as you mentioned a new more powerful pump.



The cylinder coil is a possibility, I wouldn't go with the smelling the inhibitor as 1 liter of inhibitor in 100 liters of water transferring into a 140 litre approx. cylinder of water will be so diluted I doubt you notice it. Especially when a bath may use a 100 liters of water a time.

The cylider change wouldn't be cheap so best to be sure before jumping in.


Do you have an Electric Immersion heater to heat the water?

If yes you could drain the heating system and fit 2 isolation Valves in the flow and return to the cylinder refill and temporally just use the boiler for the central heating and the electric immersion for hot water.

This way you could prove one way or the other if the cylinder ( Its coil ) is the problem. Then just open the valves if its ok and switch back to using the boiler to heat it.

My hunch is it's not the cylinder as they rarely fail this way ( does happen but not often )
Good luck

Click to expand...

Thanks very much.

I don't know if the old system was open vent or not, but there is a mix of rads (there have been three separate extensions over the years). Some of the rads are pretty old for sure. I was aware of the issue of sludge build-up so had the whole system power flushed when the two new rads were put in. He did it properly, isolating each rad in turn. I'm hoping that oxidation venting is now cured - anyway, surely that can't explain a drop in cold pressure from 1.4 bar to 0.8 bar in 24 hours??

Yes, I do have an immersion heating element - I had to have that replaced too; it was knackered. I don't use HW much - I don't bath, I (currently) have an electric shower, and use the dishwasher to do most of the washing up. What does inhibitor smell like? Is it acidic or alkali (as opposed to neutral) - I have access to litmus paper at work, so could test the PH.

I'm liking the idea of isolating the HW cylinder temporarily - do I achieve the same thing by simply switching the HW off and keeping the motorised valve closed, or do I have to fit the isolation valves?

Again - many thanks....

Goldstone1976 said:

Thanks very much.

I don't know if the old system was open vent or not, but there is a mix of rads (there have been three separate extensions over the years). Some of the rads are pretty old for sure. I was aware of the issue of sludge build-up so had the whole system power flushed when the two new rads were put in. He did it properly, isolating each rad in turn. I'm hoping that oxidation venting is now cured - anyway, surely that can't explain a drop in cold pressure from 1.4 bar to 0.8 bar in 24 hours??

Yes, I do have an immersion heating element - I had to have that replaced too; it was knackered. I don't use HW much - I don't bath, I (currently) have an electric shower, and use the dishwasher to do most of the washing up. What does inhibitor smell like? Is it acidic or alkali (as opposed to neutral) - I have access to litmus paper at work, so could test the PH.

I'm liking the idea of isolating the HW cylinder temporarily - do I achieve the same thing by simply switching the HW off and keeping the motorised valve closed, or do I have to fit the isolation valves?

Again - many thanks....

Click to expand...

No problem, If you just isolate the cylinder by turning the hot water off the motorised valve will shut off but water can stiil flow through the return pipe to the cylinder. Also the motorised valve may let by. So as you would have to fit an isolation valve on the return you might as well fit one on the flow after the zone valve also.

I know you have had it flushed but the mention of the air in the sealed system, the larger pump and some old rads makes me think of sludge. but as you say the cold drop of 1.4 to 0.8 bar goes against that.

It's definitely a tricky one. The leak in the concrete floor is a possibility but all that upheaval and cost to find and replace if it's not the problem would make me wary of going down that route until it's the last possibility.

Maybe isolate the cylinder and at least that way you know for sure if thats the problem or not and then go from there.

Good luck

How many radiators are fed from pipe work buried in the concrete floor?
Can you see a flow and return going into the concrete floor, possibly 22mm pipe?

Just wondering if the pipe work feeding the pipe work buried in the concrete can be isolated separately to the rest of the heating system.

I have done a fair few jobs where I have ran separate surface pipe work drops to individual radiators when there has been a leak in a concrete floor.
Doesn't always look pretty but it can save chopping up loads of concrete flooring.

jon12345 said:

No problem, If you just isolate the cylinder by turning the hot water off the motorised valve will shut off but water can stiil flow through the return pipe to the cylinder. Also the motorised valve may let by. So as you would have to fit an isolation valve on the return you might as well fit one on the flow after the zone valve also.

I know you have had it flushed but the mention of the air in the sealed system, the larger pump and some old rads makes me think of sludge. but as you say the cold drop of 1.4 to 0.8 bar goes against that.

It's definitely a tricky one. The leak in the concrete floor is a possibility but all that upheaval and cost to find and replace if it's not the problem would make me wary of going down that route until it's the last possibility.

Maybe isolate the cylinder and at least that way you know for sure if thats the problem or not and then go from there.

Good luck

Click to expand...

Yep - that all makes sense. I'll get the plumber to isolate the cylinder as you suggest; and go from there.

Cheers

bn9 bha said:

How many radiators are fed from pipe work buried in the concrete floor?
Can you see a flow and return going into the concrete floor, possibly 22mm pipe?

Just wondering if the pipe work feeding the pipe work buried in the concrete can be isolated separately to the rest of the heating system.

I have done a fair few jobs where I have ran separate surface pipe work drops to individual radiators when there has been a leak in a concrete floor.
Doesn't always look pretty but it can save chopping up loads of concrete flooring.

Click to expand...

Interesting suggestion. I haven't seen the pipe work going into the concrete floor, but it must do somehow. I'll have a look when I get home. There are only two rads fed by buried pipes. Surface drops would be infinitely preferable to digging up the floor. But to make that happen I have to find the flow and return where they enter the concrete, right?

Thanks v much for the reply.

Goldstone1976 said:

Interesting suggestion. I haven't seen the pipe work going into the concrete floor, but it must do somehow. I'll have a look when I get home. There are only two rads fed by buried pipes. Surface drops would be infinitely preferable to digging up the floor. But to make that happen I have to find the flow and return where they enter the concrete, right?

Thanks v much for the reply.

Click to expand...

Yes you will have to find where the pipes enter the concrete.
The pipes could be boxed in or in a cupboard, hopefully they are not buried in a wall.

I like the idea suggested by Jon, isolating the F&R to the cylinder, it's definitely worth a try.

Update:

It's not at all obvious where the f&r pipes enter the concrete - no obvious boxes, not obviously in a cupboard. I do have the invoice from the builder of this extension, so there's an outside chance they'll have records - it was done in '06. It does seem an awfully short period of time for a pipe to have corroded though...

There is already an isolation valve on the return side of the CH loop into the HW cylinder! It seems to be part of the original circuit too, not an afterthought. I'm going to close that off and rely on (hope?) the HW motorised valve not letting by if I turn the HW off. If the pressure drop is fixed by this, then I know that the problem is indeed crossover inside the cylinder, right? If the pressure drop continues, I think my next step is to try a thermal camera on the concrete floor - I've found one I can borrow for free, so I might as well have a look and see if there is massive pooling under the concrete floor - if there is, then there's little point in draining the system to fit an isolation valve on the flow side of the HW cylinder since I know that (at least part of) the problem lies under the concrete. Seem sensible?

Donation about to be made to REMF - thanks....

Goldstone1976 said:

Update:

It's not at all obvious where the f&r pipes enter the concrete - no obvious boxes, not obviously in a cupboard. I do have the invoice from the builder of this extension, so there's an outside chance they'll have records - it was done in '06. It does seem an awfully short period of time for a pipe to have corroded though...

There is already an isolation valve on the return side of the CH loop into the HW cylinder! It seems to be part of the original circuit too, not an afterthought. I'm going to close that off and rely on (hope?) the HW motorised valve not letting by if I turn the HW off. If the pressure drop is fixed by this, then I know that the problem is indeed crossover inside the cylinder, right? If the pressure drop continues, I think my next step is to try a thermal camera on the concrete floor - I've found one I can borrow for free, so I might as well have a look and see if there is massive pooling under the concrete floor - if there is, then there's little point in draining the system to fit an isolation valve on the flow side of the HW cylinder since I know that (at least part of) the problem lies under the concrete. Seem sensible?

Donation about to be made to REMF - thanks....

Click to expand...

That's great news. Yes you should be able to turn the hot water off and shut the isolation valve on the return off. If the pressure drop stops then it is the coil ( crossover ) in the cylinder that is the problem.

The isolation valve that is fitted to the return was probably installed ( good practice ) as a balancing valve. This is used to control the rate at which water flows through the cylinder. Like the radiator valves on the opposite end to where you turn the rads on and off which are used to balance/control the flow to each radiator. Basically stops a radiator or cylinder getting too much of the boilers heat.

All you need to do is when you isolate the valve on the return just note the how much it is open. just count the number of turns it takes to turn off. It will probably be set at about halfway.


Bn9 BHA's idea to run surface pipework is a good one if it does turn out to be a leak in the concrete floor. It would save a lot of upheaval.

Also as you can borrow a thermal camera for free thats going to help. If you turn on the heating when using the camera it may also help you trace where the pipes enter the floor. Maybe where the original wood floor meets the new concrete floor.

Fingers crossed!