Glowworm 30cxi and dropping pressure (Parts replaced)

17 Feb 2008
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United Kingdom
Hi All,

I recently had a problem with my Glowworm 30cxi boiler (leak) and had to replace the Left Hand Hydroblock(Sanitary Block). After replacing this part everything seemed fine for a few days then the CH pressure started to drop until the boiler became inoperable. Everything started working again after refilling the system back to 1 bar but the pressure would drop and I'd have to repeat the refilling.

After reading extensively on this site (Thanks to all who posted) I tested and replaced a faulty Expansion vessel (I checked the pressure was 0.5 bar before/after fitting) and replaced the Safety Discharge Valve (PRV) just in case. Unfortunately the boiler is still dropping pressure. I have noticed that a lot of water is ejected from the external plastic condensate pipe.

I'm presuming that the water from the condensate pipe is the leaking water from the boiler but I'm at a loss to explain why it's still being ejected and what I can do to stop it. Can anybody help.

Thanks in advance
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Sounds like you have a leaking heat exchanger, and the water is running straight out the condense pipe.

See if when you isolate the boiler it should eventually stop, and nothing should come out the condense unless the boiler is running.

Thanks for your quick reply :)

I undid the yellow cap on the bottom of the condensate reservoir and it only drips water when the heating is on if that is what you mean. Is it usual for so many parts to fail at the same time? Can the heat exchanger be fixed or is it a replacement?

Can anybody tell me if I can externally test my heat exchanger before I order a new one. At £105 I'd like to be sure that it is faulty.

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Sorry to be a pain but can anyone answer my question. If I need the heat exchanger i'd like to order it ASAP so I can fit it on the weekend.

Thanks in advance
I'd be looking for a leak on the central heating system before replacing any heat exchanger.

The CXI main heat exchanger is Stainless steel and I have not had one leak YET! If you say it only drips when heating is on this can probibly be ruled out

Try internal leak sealer through the rads first.

The second point is that the £105 you were quoted is for a dometic hot water heat exchanger....the main heat exchanger for these is £300 +++

Finally if all that fails it could be your CH water passing through your HE to the domestic hot water

As I said, simple first step look for leaks under floor or try leak sealer first and see how you go!
can anyone tell me what the plastic thing is called that is attatched to the stainless steel heat exchanger? cheers
I don't think it's a leak in the radiators/pipes as if the boiler isn't switched on the pressure stays at 1 bar. Also if I put a jug under the outside plastic condensate pipe there's a lot of water ejected into it whereas I never noticed the drain being wet before I replaced the parts. Anything else it could be besides the expensive heat exchanger?

Which side of the boiler is the plastic part your after on, the left or right and do you mean the large black plastic part which most of the pipes plug into?

Isolate the boiler by turning the flow and return valves off ,turn the heating off as well.If the pressure drops then you have a leak boiler side,check the prv and the condesate pipes.If the dhw heat exchanger is cracked then the pressure of the mains will push the system pressure up not down.If when you open the valves the pressure drops then you have a leak system side.This is assuming the valves are not letting bye.
Thanks to all who have replied. I intend to investigate all the above this weekend and will keep you all updated.

Thanks in advance
If the dhw heat exchanger is cracked then the pressure of the mains will push the system pressure up not down.

Not true, I have seen on a few occasions the presssure dropping from a leaking DHW HE, like a venturi effect??

You think it might not be pipework but the extra force could cause the leak to only be apparent on the CH system when on, but as suggested isolate the boiler and leave overnight, see if its dropped.

Good luck!!
Well you were correct in that I had a leak on an elbow joint. I've renewed the elbow and hopefully this will stop the pressure drops. I wonder why I had all the problems at the same time. Before the failed sanitary block I had no problems with leaky pipes.

Thanks to all who replied it's much appreciated.
I see you had to replace your Left Hand Hydroblock - I need to do the same thing.
I've been quoted £225 (exVAT) for the part - does that sound right or should I shop around?

That's a ridiculous price :eek: I paid £111.87 inc vat and delivery from a company called Lincs Gas whom I found with a google search. The part was brand new and genuine. I'm not affiliated with them in anyway except as an impressed customer. I hope it's alright to provide company names etc.

Hope this helps

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