Worcester Greenstar HE 35 Plus - losing pressure

22 Jan 2007
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United Kingdom
I've had my Worcester Greenstar boiler installed and working well for over 10 years now.

Late last year it started to lose pressure slowly.
Water was leaking out of the overflow outside.

A local Worcester recommended plumber came and serviced it and replaced the pressure relief valve. This slowed the pressure loss for a while.

However the pressure/water loss has increased and now means I am having to top it up at least once a day. It drops from ~1 or 1.5bar to zero in a few hours.

No water is leaking out of the overflow outside. I did tie a bag over the condensate drain into the sink overflow, and overnight (with heating on low) it did collect about half a pint of water.

I've previously inspected as much of the groundfloor radiator pipework as I can, and found no leak. Though to be fair that was before Christmas when the leak was much slower.

Is there anything I can do to be certain that it is a radiator leak or a boiler problem? e.g. isolate the bolier from the pipework, to see if I still get a pressure drop? I understand I would need to turn the boiler off while doing this.

Obviously if it's pipework, I need to be getting floors up :(
If it's the boiler e.g. faulty heat exchanger I would get a Worcester Engineer in to fix it. Problem is I don't want to pay Worcester £230 for them to tell me it must be a leaky pipe.

The local plumber is suggesting the best option is leak sealant.

Any suggestions would be very helpful.

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When you say heating running low do you mean room thermostat on low or the thermostat for the radiators on low??? if the boiler is running and it's low you will collect condensate and more of it.

You need to charge your boiler up to pressure and isolate it from the mains.

Locate the heating flow and return valves under the boiler and turn them off (they are usually quarter turn) and leave the boiler for period overnight.

If it remains at pressure then the leak is on the system if the boiler pressure still drops then it's on the boiler

This should then point you better to what you can do
If it's on the system then you could try leak sealer however depends how fast the pressure is lost as to whether it forms a seal or not
If you fill it to 1 Bar when cold, what pressure does it go to when the heating is up and running and the boiler is hot ?

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Isolate the flow and return pipes with the boiler pressurized up to 1 bar and turned off, leave it for 12 hours with a cotainer inder prv termination. If your pressure has dropped and no sign of a leak around the boiler or from the prv pipe suspect your heat exchanger is cracked. If the pressure is the same start lifting boards to find your leak.
Thanks for all the advice.

I plan to test the pressure loss tomorrow. While waiting I'll have a look at the pipes that are easy to get to...

Pressure loss is now quick i.e. from 1bar to nothing in a few hours.

A plumber renewed the PRV before Christmas.

Not tested pressure loss from cold, as we tend to leave the heating on to maintain a minimum temp for the kids bedroom. Doesn't go near the 3 bar to activiate the PRV.
the first guy who came and replaced the prv should have also checked the expansion vessel charge. when a prv activates, dirt can sometimes stop it from sealing again properly, even if its a new one.
run the central heating and check the prv pipe outside and see if its dripping.

do this first before you start messing about with floorboards and chucking leak sealer at it, you are more likely to bung summat up in the boiler with it.
Well I isolated the boiler from the heating pipes and the system still lost pressure quickly. In fact I was getting a lot of water down the condensate pipe even with the boiler switched off.

Called in the Worcester engineer. He arrived this afternoon and fitted a new heat exchanger. The price of the part was much more than the call-out fee, so I don't feel too bad. Also I didn't fancy getting floorboards up everywhere!

He is returning tomorrow as although the heating now works, the hot water now doesn't. I guess that will be something simple.
Test the expansion vessel. Remove the little cap of the valve and press the little pin for a second or so. If air is coming out it is okay. Then check the pressure in the vessel using a suitable gauge. If pressure is less than 1 bar, top it up using a pump with a suitable gauge. If water is coming out of the valve, its a knackered vessel. Replace it.
That was all lat January!

I expect its all sorted out now!

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