Strange pressure drops

[mattyboyq]

This is something I have been battling against for 3 years!

If someone can help I would be eternally grateful.........

Our heating system was not working - poor pressure in the system, radiators were not getting warm. After the usual attempts to improve this we had the system pressurised with an expansion tank etc. The system ran much better after that. Then we had problems with dropping pressure (only after the heating went off!) and a fault on the boiler. After more investigation and battling, my wife actually discovered that water was running out the main drain pipe when the heating went off. We were advised to get a new heat exchanger which we did. This helped sort the boiler problem. We were okay with just the hot water on over th summer.

Now we have the heating back on, the pressure, set at 1.5 bar drops doen to 0 after 2 or 3 runs. It needs constant topping up. The pressure drop only happens after the heating goes off and only once the water seems to have cooled. What is going on?

Most/everyone insists that there is a leak, somewhere (no evidence so far). The thing I can't figure out is that water still seems to come down main drain pipe once the heating cools - about 3 or 4 litres! I know that there will be some water from condensation, but not this much.

Does anyone know why this might be? The only suspicion I have is that it might be the temperature/pressure valve somewhere?

Please help!

 

[CBF]

what boiler have you got, was it a sealed system before or did you just change the old boiler into a sealed one or did you get a new boiler ??

 

[45yearsagasman]

I would suspect the expansion vessel, but more worrying is the fact that you have been topping up the system for 3 years and no mention of inhibitors.

 

[mattyboyq]

what boiler have you got, was it a sealed system before or did you just change the old boiler into a sealed one or did you get a new boiler ??

It's a Gloworm Flexicom. I think it was new about 4 years ago. It wasn't sealed, we changed th old one over.

 

[mattyboyq]

I would suspect the expansion vessel, but more worrying is the fact that you have been topping up the system for 3 years and no mention of inhibitors.

I've been 'assured' it won't be the expansion vessel. We've only been toppin up for 8 months (still a lot, I know) but who know what was going on when the system was just being tank fed.

I'm testing now to see if the water is coming from what I think is the condensation pipe.

 

[45yearsagasman]

What Flexicom you do you have?

 

[mattyboyq]

What Flexicom you do you have?

18HX

 

[mcmoby69]

turn the heating stat down. pressurise the system. does water flow out of the condense pipe, and does the pressure drop?

 

[mattyboyq]

turn the heating stat down. pressurise the system. does water flow out of the condense pipe, and does the pressure drop?

Is that with the heating on?

 

[doitall]

I've been 'assured' it won't be the expansion vessel.

By the same 2-3 plumbers that can't find a leak, or offer an alternative suggestion.

 

[mattyboyq]

I would suspect the expansion vessel, but more worrying is the fact that you have been topping up the system for 3 years and no mention of inhibitors.

I've been 'assured' it won't be the expansion vessel. We've only been toppin up for 8 months (still a lot, I know) but who know what was going on when the system was just being tank fed.

I'm testing now to see if the water is coming from what I think is the condensation pipe.

Turned heating off yesterday Heating went off at at 1200 and the pressure was 1.3 bar. By 4.50pm it was 1.15 bar. The heating/HW came on by 6.15 it was 1.31 bar. The pressure then dropped off to 1.2 bar.

The heating went off at 8.00pm the pressure dropped to 1.05 by 11.30pm. In the morning the pressure was 1.02 bar (after heating had been on in the early morning but was off by then.). By 2.30 the pressure was 0.9 bar and the heating was turned on. By 3.00 the pressure was 1.05 bar. It stayed arounf 1 bar until 800pm when the heating went off. By 11.30pm it ws 0.6 bar. At 6am it was 0!

I collected about a quarter of a bucket of water from the condesation pipe but the heating was on for about 8 hours so I would expect something like that. It only dripped when the heating was on (contrary to what I thought had been happening.)

The pressure seems to drop after the heating is on, not during, and drops less when the pressure is higher (once it is at less than 0.8 bar it seems to drop quite quickly).

Still seems like a leak?

 

[mcmoby69]

turn the heating stat down. pressurise the system. does water flow out of the condense pipe, and does the pressure drop?

Is that with the heating on?

heating off.

while you are running the boiler on CH you will struggle to find the cause of the leak. the pressure goes up and down as the CH water heats up and cools down, thats why your readings are up and down. you need to do these tests with the boiler pressurised and cold. once you know its not leaking when its cold, thats when you start testing it when the heating is on.

pressurise it, leave the CH off. check the condense pipe to see if there is any water trickling,(there shouldnt be) and the pressure should not drop. if it does there is an internal leak on the boiler

if there is no drop then turn the heating on. when the system is hot, have a look at the blow off pipe to see if it is dripping. tape a poly bag to it, it should not fill up. if it does then the expansion vessel is either goosed or needs recharging or the PRV needs replacing

 

[mattyboyq]

turn the heating stat down. pressurise the system. does water flow out of the condense pipe, and does the pressure drop?

Is that with the heating on?

Heating off, stat down, watching pressure and condensation run off.

 

[mattyboyq]

turn the heating stat down. pressurise the system. does water flow out of the condense pipe, and does the pressure drop?

Is that with the heating on?

heating off.

while you are running the boiler on CH you will struggle to find the cause of the leak. the pressure goes up and down as the CH water heats up and cools down, thats why your readings are up and down. you need to do these tests with the boiler pressurised and cold. once you know its not leaking when its cold, thats when you start testing it when the heating is on.

pressurise it, leave the CH off. check the condense pipe to see if there is any water trickling,(there shouldnt be) and the pressure should not drop. if it does there is an internal leak on the boiler

if there is no drop then turn the heating on. when the system is hot, have a look at the blow off pipe to see if it is dripping. tape a poly bag to it, it should not fill up. if it does then the expansion vessel is either goosed or needs recharging or the PRV needs replacing

What does 'internal leak on the boiler' mean? Is that a leak in the heating system somewhere? (i.e. under floorboards or something?)

 

[mcmoby69]

internal leak on the boiler means, inside the boiler not under the floorboards etc, that would be the ch system.