Hot water cylinder not getting to temperature

14 Jun 2006
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United Kingdom

Hoping someone can help.

Have recently moved into new house with a glowworm Ultracom 18Hxi boiler/

Issue I have is the hot water is not getting to temperature of 60C set on cylinder stat - the cylinder stat is new, I measured the tank temperature with a temp probe on my multimeter and it reads around 50C and if I move the stat to 50C the boiler and pump turn off as expected.

So, with just the HW turned on at the timer the pump runs continuously for hours as I guess the HW stat is constantly calling for heat, but tank never gets to 60C...

The boiler is set to 75C, I notice when it fires up it only burns for say 30 seconds, quickly hits 75C on the display and turns off however measuring the inlet and outlet pipe temps it doesn't seem to be 75C.

If I turn the CH on as well at same time the boiler burns for much longer and the temp display on it climbs much slower.

Any ideas? Is this a boiler issue?

The system has been powerflushed as well and its had a new 3 way valve as that wasn't working correctly either. Tried pump (also new) set on 1 and 2 same issue.

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Is there a balancing valve on the HW circuit, if there is try opening it a bit.
Sorry don't know, what would a balancing valve look like and where would it be positioned?
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put the pump on 3 & see if that makes any diff sounds like a lack of circulation to me
Next to cylinder, usually.

There is a gate valve on the lower pipe that comes out from the cylinder, presumably the return from the heat exchange loop (the top pipe goes in about half way up and has a bleed valve on it also).
put the pump on 3 & see if that makes any diff sounds like a lack of circulation to me

OK will try that, presumably I just need to make sure it doesn't cause venting into the HW feed tank in the loft?
if it does then the pipework isn't installed correctly or you have a restriction somewhere
OK, I will separately try pump on 3 and opening the cylinder return gate valve a bit - anticlockwise I presume.
As been said, open the gate valve a bit more, count the number of turns so you can put it back if needed.

You will know when it's working as the flow pipe to the cylinder will get too hot to hold.

Is the bleed valve manual or auto? If manual, open and check for air, should just be water coming out.
Thanks all, I will try the suggestions.

Yes, the system is quite noisy so I suspect a lot of air may be trapped then.

Do you bleed the pump when its running and the same question about the bleed valve on the cylinder HW feed ?
Waking up this thread, thanks to all the previous help which partially sorted the issue but in the end I moved my tank thermostat down to 55C so the boiler and pump eventually stop.

Can I ask, I find whenever the system has been drained and then refilled it seems to get completely full of air and this problem reoccurs, as its an open vented system shouldn't the air just dissipate up the vent pipe ?

Pictures here //


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