Slow pressure drop on worcester bosch boiler

[denso13]

Also according to boiler sizing a 14 rad property should have a 30 kW boiler not a 18/25 kW boiler so the boiler itself is undersized. And the rads themselves are oversized

At an average of 1kw per rad, which is normally adequate, it would need a 14kw boiler, 18/25kw should be fine.

 

[TryAgain1]

Yes, try that.

Yes, or tie a plastic bag over it.

Tried it

Boiler heating loop isolation test carried out from 2100 11/10/26 to 0900 12/10/26. On 11/10 I increased pressure to 1.5 bar in heating loop then isolated Flow/Return (2m from boiler) 2100 turned boiler off. Inspected 0900 12/10/26 pressure had dropped to just below 1 bar (boiler turned off all night, temp about 20/30 degrees). When turned boiler back on the temperature crept up from about 20/30 degrees C to 70 degrees C with the final pressure about 1.6 bar.

So the pressure swings from 1 bar (boiler turned off) to 1.5/1.6 bar (boiler fired on).

No leaks (so far) on the radiator side

I looked in the PRV discharge line and there was no water/fluid in the bag taped over the end

Is this a EV issue?

 

[Johntheo5]

Tried it

Boiler heating loop isolation test carried out from 2100 11/10/26 to 0900 12/10/26. On 11/10 I increased pressure to 1.5 bar in heating loop then isolated Flow/Return (2m from boiler) 2100 turned boiler off. Inspected 0900 12/10/26 pressure had dropped to just below 1 bar (boiler turned off all night, temp about 20/30 degrees). When turned boiler back on the temperature crept up from about 20/30 degrees C to 70 degrees C with the final pressure about 1.6 bar.

So the pressure swings from 1 bar (boiler turned off) to 1.5/1.6 bar (boiler fired on).

No leaks (so far) on the radiator side

I looked in the PRV discharge line and there was no water/fluid in the bag taped over the end

Is this a EV issue?

If you increased the boiler pressure to 1.5bar while cold and it then fell to 1.0bar then you will have lost a substantial 2.4L. IF "So the pressure swings from 1 bar (boiler turned off) to 1.5/1.6 bar (boiler fired on)." and if that means that the cold pressure is 1.0bar and the hot pressure is 1.6bar with the system up to temperature and then returns to 1.0bar when cold then that suggests that the charging/filling pressures are the same (at 1.0bar) so this would be normal under these conditions.. You should ensure no pressure at the EV water (boiler) end, then get a tyre pressure gauge and check the EV air end pressure at the schrader valve, ensure its (air) pressurized to 1.0bar, fill/pressurize the water end to 1.5bar and monitor it again, the pressure should rise to ~ 2.6bar when hot and reduce to 1.5bar when fully cold, if it eventually reduces again to 1.0bar then you have a leak somewhere as there is nothing coming from the pressure relief valve. The leak might be from the boiler combustion chamber, you might then see a leak into the condensate trap.

 

[Exedon]

Have a really good look round base of boiler .
The Worcester oil combi's are know for leaking. Check carefully round heat store.
We have pulled out a number at 5 to 6 years old.
Also expansion vessels fail with horrible regularity.

 

[TryAgain1]

If you increased the boiler pressure to 1.5bar while cold and it then fell to 1.0bar then you will have lost a substantial 2.4L. IF "So the pressure swings from 1 bar (boiler turned off) to 1.5/1.6 bar (boiler fired on)." and if that means that the cold pressure is 1.0bar and the hot pressure is 1.6bar with the system up to temperature and then returns to 1.0bar when cold then that suggests that the charging/filling pressures are the same (at 1.0bar) so this would be normal under these conditions.. You should ensure no pressure at the EV water (boiler) end, then get a tyre pressure gauge and check the EV air end pressure at the schrader valve, ensure its (air) pressurized to 1.0bar, fill/pressurize the water end to 1.5bar and monitor it again, the pressure should rise to ~ 2.6bar when hot and reduce to 1.5bar when fully cold, if it eventually reduces again to 1.0bar then you have a leak somewhere as there is nothing coming from the pressure relief valve. The leak might be from the boiler combustion chamber, you might then see a leak into the condensate trap.

I can't see inside the Worcester heatslave unless I remove the EV. From what I saw the EV's schrader did not have escaping air could not see damp on bottom of oil boiler. There is a drain valve at the front

If you increased the boiler pressure to 1.5bar while cold and it then fell to 1.0bar then you will have lost a substantial 2.4L. IF "So the pressure swings from 1 bar (boiler turned off) to 1.5/1.6 bar (boiler fired on)." and if that means that the cold pressure is 1.0bar and the hot pressure is 1.6bar with the system up to temperature and then returns to 1.0bar when cold then that suggests that the charging/filling pressures are the same (at 1.0bar) so this would be normal under these conditions.. You should ensure no pressure at the EV water (boiler) end, then get a tyre pressure gauge and check the EV air end pressure at the schrader valve, ensure its (air) pressurized to 1.0bar, fill/pressurize the water end to 1.5bar and monitor it again, the pressure should rise to ~ 2.6bar when hot and reduce to 1.5bar when fully cold, if it eventually reduces again to 1.0bar then you have a leak somewhere as there is nothing coming from the pressure relief valve. The leak might be from the boiler combustion chamber, you might then see a leak into the condensate trap.

The boiler unit has little/no space under the casing I would have to remove the EV to see. The EV's schrader looks OK and I could not see the bottom of the unit on the floor properly for leak check. There is a drain valve (see pic) at the front could not see any sign of use so not likely leaking. The PRV is at the back of the boiler I think. Would an infra red camera help see if there are leaks? I'm going to install a secondary EV anyway on the Return line so will have to drain down system so can check main EV then.

 

[TryAgain1]

Have a really good look round base of boiler .
The Worcester oil combi's are know for leaking. Check carefully round heat store.
We have pulled out a number at 5 to 6 years old.
Also expansion vessels fail with horrible regularity.

This is all I can see without removing the EV does not appear to be any leaking. There is a red/brown residue on the floor from the last boiler man visit.

 

[TryAgain1]

Can I install a Zilmet trade tech 18/24 litre secondary expansion vessel on the Return line (see pic for Zilmet). I would have an isolation valve and drain valve before going into the secondary EV. There is space on the breeze block wall (nowhere near electrics in case of EV leak) for installing a secondary EV about 1.5m off ground.

 

[CarloHeatingEng]

Tried it

Boiler heating loop isolation test carried out from 2100 11/10/26 to 0900 12/10/26. On 11/10 I increased pressure to 1.5 bar in heating loop then isolated Flow/Return (2m from boiler) 2100 turned boiler off. Inspected 0900 12/10/26 pressure had dropped to just below 1 bar (boiler turned off all night, temp about 20/30 degrees). When turned boiler back on the temperature crept up from about 20/30 degrees C to 70 degrees C with the final pressure about 1.6 bar.

So the pressure swings from 1 bar (boiler turned off) to 1.5/1.6 bar (boiler fired on).

No leaks (so far) on the radiator side

I looked in the PRV discharge line and there was no water/fluid in the bag taped over the end

Is this a EV issue?

That 1.6 hot from 1.0 cold is a normal rise, so your vessel’s doing its job. It also means your overnight test may not have shown a leak at all. If you topped up to 1.5 while it was still warm, just under 1 cold is where it would settle anyway. Redo it like for like: fill with the system cold, isolate, boiler off, and read it cold next morning. That gives you a real number before you drain down and spend on a second vessel.

 

[TryAgain1]

That 1.6 hot from 1.0 cold is a normal rise, so your vessel’s doing its job. It also means your overnight test may not have shown a leak at all. If you topped up to 1.5 while it was still warm, just under 1 cold is where it would settle anyway. Redo it like for like: fill with the system cold, isolate, boiler off, and read it cold next morning. That gives you a real number before you drain down and spend on a second vessel.

An undersized expansion vessel seems to be a common issue and I need to extend the life of this boiler and if spending £60 buying a secondary expansion vessel extends the boiler a few years more (e.g. saves pump from failing) then why not

Can the Zilmet trade tech 18/24 litre secondary expansion vessel be used on heating systems?

 

[CarloHeatingEng]

Yes, the Trade Tec is a heating vessel, so that’s fine on the return. It comes pre-charged at 1 bar, which suits a system like yours, so no need to touch it. You can’t have too much expansion, but bear in mind more vessel also makes a slow leak drop the gauge slower, so keep an eye on it after rather than assume it’s cured. And leave the isolating valves open once it’s refilled.

 

[TryAgain1]

Yes, the Trade Tec is a heating vessel, so that’s fine on the return. It comes pre-charged at 1 bar, which suits a system like yours, so no need to touch it. You can’t have too much expansion, but bear in mind more vessel also makes a slow leak drop the gauge slower, so keep an eye on it after rather than assume it’s cured. And leave the isolating valves open once it’s refilled.

Is it worth replacing the schrader valve and charging the main EV to 1 bar whilst I'm adding the secondary Trade Tec EV? The main EV was charged in mid 2024 but it was whilst the boiler was not drained down nor isolated