Glowworm Combi Boiler - Hot Water problem

[John560]

I have a Glowworm Combi which is very slow to allow hot water through.
Initially when the hot water is turned on there is a good flow of water but it's cold. It doesn't matter how long the tap is left running, the water remains cold. If I turn down the flow and leave it running very slowly for a while eventually the water will run hot. I can then turn the tap full on and I'll get a full flow of hot water. The problem only happens in the bathroom both the bath tap and the shower. The kitchen tap is fine. Does anyone have any ideas?

 

[poolebybirth]

what make is it mate? I mean what Glowworm boiler is it/

 

[45yearsagasman]

It would help if you said what model you have

 

[poolebybirth]

could be taking a while to drain the cold in the pipe before the hot comes through - could also be other things!

 

[John560]

Sorry for the delay in responding. I guess it's time for a confession. This isn't actually my system. It's belongs to a close friend of mine which is why it took a little while to get the information. He tells me it's a " Glow Worm Compact Electronic". No model number though. The way he described the problem it doesn't sound as though it's just a delay in the water coming through the pipes from the boiler. If anything it sounds a bit like the diverter valve is playing up except that he says if he leaves the hot water running very slowly after a time (which can be up to 20 mins) the water will start to run hot. It's also a little odd that the problem only happens in the bathroom not the kitchen. One thing I have found out is that they are in a very hard water area and I wonder if lime scale might be at the bottom of the problem somewhere. He has contacted a Plumber recently who said it didn't sound like a boiler problem to him. The plumber hasn't looked at it because he didn't want to change a call out fee for no reason. The intent of the post was in the hope that someone might have solved a similar problem in the past with a combi.

 

[lukachu]

Hi John, did you get this problem resolved? I have exactly the same issue and was wondering what I should do.

I've just had a plumber who said that I need a new circuit board and it would cost £300 plus VAT

 

[John560]

Hi. I don't thnk think problem is solved. As I said in my prior post this isn't my boiler so the issue tends to slip off the table for me until I see my mate again. Coincidentally I'm going over to his house next Thursday so I'll take a close look then. I wouldn't change the circuit board unless there was some corroborating evidence such as a error message on the LED (if it has one). The really odd thing about my mates problem is that he says he doesn't get the problem with the kitchen tap only the bathroom/shower. One test worth doing is that if you have the hot water running and it's running cold give the top of the diverter valve a little twist. If it's anything like my Vailant the end will turn quite freely. If its sticking this will free it up and so you will get hot water immediately. This is one of the things I'm going to look at on Thursday. If it's the diverter valve they are a lot cheaper than a new board. I'll post again after Thursday. Meanwhile if you get any more info please let me know as I would like to help my mate out if I can.

 

[lukachu]

I have since been advised by a different plumber that I do not need a new PSB - apparently if it was broken, the boiler would shut off hot water to all taps and I'm still getting very hot water in the kitchen. I was advised that it may be an airlock, so did the following:

- turned off the boiler at the socket
- put a towel around the bathroom mixer tap
- opened the hot and cold tap and tried to force the airlock back through the pipes. I did this for 5 mins

This didn't work, so I ran the hot taps in the bath and bathroom sink for 15 mins. This also didn't work.

I've since noticed a dribble coming from the control unit of my shower, so i'm going to investigate whether this is all down to a pressure issue. I'll keep you updated

 

[John560]

Hi It's very unlikely that you will have an airlock on the hot water side as the pressure will flush any air out when any of the taps are turned on. I don't really understand what you mean by the control unit. If your system is over pressuring you should see this in the pressure gauge. If the pressure keeps climbing there are a couple of tests you might be able to do to find out what is causing the problem. My instinct is that you have the same problem that my mate has which is the diverter valve isn't sensing the pressure change when you turn on the taps that are a distance away from the boiler. Did you try twisting the top of the diverter valve? I had a similar problem with my vaillant and turning the top of the valve slightly seems to have cured the problem completely (for the time being).

 

[lukachu]

can yo please explain what you mean by the divertor valve?

 

[John560]

The diverter valve is the component that changes the water going through the heat exchanger from the hot water to the central heating. Basically its a pressure switch operated three way valve. They only apply to combi boilers and the do tend to be a bit temperamental. If you drop the control box down it's a large brass component and its usually situated at the front of the boiler so its easy to dentify. To get a feel for what it look like just type 'Glowworm diverter' valve into your search engine and click images. This should give you a picture that looks something like the one in your boiler.

 

[Agile]

I have since been advised by a different plumber that I do not need a new PSB - apparently if it was broken, the boiler would shut off hot water to all taps and I'm still getting very hot water in the kitchen.

Well as none of the things he tried worked then perhaps you do need a new PSB ?

But I can say with some surety that what you definitely do need is a new boiler engineer. ( They are better with boilers than plumbers are ).

Tony

 

[lukachu]

thanks i'll give it a try tonight and let you know if it works - good luck with your mate's boiler

 

[lukachu]

Hi John, did you have any luck with your friends' boiler?

 

[John560]

I haven't been over their yet. First both myself and my wife caught this cold that's going around. We were OK but my mates health is such that it takes him a while to get over colds etc. Then they both came down with a different bug. He did phone this afternoon (I missed him) so we should be going over in a few days. I'll post again when I've been over there. The advice given by Agile is also good. Boiler engineers do spend a lot of time looking at different boilers and so pick up a lot of tips and ideas.