Combi hot water temp probs

[beefster]

I have a 5 year old Glow worm compact 100e boiler that only feeds DHW to one bathroom with a shower and a basin.

In recent weeks i have noticed the water temp in the shower fluctuates quite a bit. I have also noticed when others use the shower the burner on the bolier pulses on and off rather than modulating the burner to control the temp. This is what i assume is causing the temp to fluctuate. I have since tested it when the hot tap in the basin is run and it does exactly the same which removes the shower control from the equation. It also occurs when both outlets are fully open? It has been fine previously with the shower used approx twice daily. We did re decorate the bathroom and it was out of use for 2 weeks just before this happened..... could something have seized up that quickly through the lack of use. seems a bit far fetched???

The water flow is more than adequate. No other outlets are being operated in the house either hot or cold....... thus the water pressure through the boiler is not fluctuating. The boiler does not lock out and this occurs when the heating demand is on or off.

Any ideas???

 

[Rob]

does this model have the HW heat exchanger? if so its blocked.

 

[beefster]

Yep, has a "plate to plate heat exchanger.

Can it be unblocked or is it a replacement job??? I assume this will be scale??

Now you say that it does sound as if the water flow within the boiler is noisier than i remember it being.

In order to understand how you came to this and not to question your answer.......

If the heat exchanger is blocked does this not mean a reduction in the flow? The flow seems ok?? Although I suppose if it has reduced gradually i may not have noticed?!

Thanks for the advice.

 

[corgiman]

I think he means that the primary side could be blocked up (the side that circulates around the boiler and heats up your water)

if the systems was not cleaned properly and ihibiter levels kept up then these are prone to blocking, and this results in the primary water getting to hot too kwik and causing the burner to switch off, ergo you get cold water at your taps

 

[beefster]

Ta for the info.

I would be surprised if it is that as the system has been drained 3 times in the 5 years it has been in and inhibitor has been added on each occasion.... I did it myself. The last time was 2 years ago approx.

If it is the primary side i would assume a good flush though might solve the problem?? Drain down.... flush...... add flushing / cleaning agent etc and refill with inhibitor in a few days??

 

[beefster]

Bear with me as i am just trying to understand the theory here..

If the primary side is blocked - there would be a lack of flow thru the heat exchanger and the boiler. This causes the boiler to overheat and shut down on the primary side water temp. Then the primanry water temp cools and the boiler is then recalled and therefore the cycle starts again.

This would then see the DHW temp cycle from hot to cold to hot to cold.

Which is what is happening. Have i got that right?

And the cure is..... flush (£20) or remove the heat exchanger (£125) ?????
Whats the recommendation from those in the know?

Thanks both for the replies and help.

 

[ChrisR]

You got it. In situ or remove and clean. Careful, unusual seals not available separately.

 

[beefster]

I will try the in situ flush through first then.

Thanks all.

 

[jocojohn]

Hi Beefster,
Could you report back on the outcome of flushing the system and which way you did it ( flow to return or vice versa ) as I have exactly the same problem with my glow worm 24 ci ( see recent posts) Thanks, Jocojohn.

 

[beefster]

Cant you do it and report back to me.... I would much prefer that

Just a thought..... I think i am right in saying that the heat exchanger is only in the primary circuit when there is a demand for DHW? Thus to get the flushing agent thru the exchanger the diverter valve will need to be operated continually. Is there a simple way to do this or do i have to leave the tap running..... Can i manually operate the valve??

Has anyone succeeded in this previously or am i wasting my time....

 

[HarrogateGas]

You got it. In situ or remove and clean. Careful, unusual seals not available separately.

The are if yoo go to parts centre (wolsley) and ask for the washers off a Chaffataux ...........same washers and were in stock too!!

 

[beefster]

Well I bit the bullet and took the heat exchanger out. I thought flushing would prob be a waste of time and it proved so. The debris was quite substantial and i doubt it would have been flushed up and out.
My boiler is top fed via a mod kit which was a pain as the additional pipes thru the boiler prevent the exchanger being removed so they had to come out....... but the boiler is in a corner..... so one could not be accessed...... so the diverter valve had to come out! Anyway its all back in and working fine. I hadnt realised how much colder the water had got...... its red hot now and all running fine.

I flushed the exchanger with water and then left it for an hour or so with neat sentenial sludge / debris remover in it. Then flushed it again and got lots of what looked like black scale out of it. Giving it a tap loosened even more....

I have one small weeping joint going into the bottom of the diverter valve which i cant seem to cure. Its a drip every 5 / 10 mins so hoping it will take up...... please!

Thanks very much for all the advice. I think you have saved me a few bob and I've learnt a bit too.

Cheers
Kev.