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Tim JA
Tim JA, HVAC Technician
Category: HVAC
Satisfied Customers: 3266
Experience:  Owner at Self-employed
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I have a Greenstar 8000 boiler but I cannot adjust the DHW

Customer Question

I have a Greenstar 8000 boiler but I cannot adjust the DHW temperature on it. When I select water I get a dashed line then it reverts to the radiator symbol
JA: Are you getting any error codes or blinking lights on your boiler? How old is it?
Customer: No error lights - Fitted in Feb this year
JA: How long has this been going on with your boiler? What have you tried so far?
Customer: I have only just tried to adjust it because the DHW is scalding. Tried nothing yet
JA: Anything else we should know to help you best?
Customer: Its connected to a Gledhill Lite Plus Hot water Storage tank
Submitted: 15 days ago.
Category: HVAC
Expert:  Tim JA replied 14 days ago.

Good evening, and welcome to the Technical section in Just Answer, an independent paid question and answer platform that matches customers' questions to experts in various skills. My name is ***** ***** I'll be happy to help you today.

I'm sorry to hear of your hot water problem.

Since you have stored hot water you should not alter any boiler settings; those settings should have been set by the system installer to suit your installation.

If the temperature of your hot water isn't being correctly regulated, then the most likely cause is one of the following:

1. A stuck motorised zone valve;
2. A faulty cylinder thermostat.

Customer: replied 14 days ago.
I can check the water temperature at the tap - The reading at the moment is 68 degrees. Do you think that is too hot?
Expert:  Tim JA replied 14 days ago.

68 is abnormally hot, yes.  Do you think there was a sudden change in the behaviour of the system, or gradual?

Do you have a multimeter or equivalent, for carrying out electrical fault-finding?

Customer: replied 14 days ago.
It seems to have happened whilst we were away on holiday - I do have a multimeter.
Expert:  Tim JA replied 14 days ago.

You have a choice of ways to start.  Personally, I would check the operation of the MZV first.  If you tell me the make and model I can give you detailed guidance?

Customer: replied 14 days ago.
Its A: EHE0200156 2 Port Motorised Valve
Expert:  Tim JA replied 14 days ago.

OK.  That's a kind of cheap copy of a Honeywell product..  Bear with me and I'll send you the guidance...

Expert:  Tim JA replied 14 days ago.

Here are the steps.

1. Power off the heating system, for safety.

2. Following the instructions in the following document to unmount the actuator.

When removing the actuator, you might need to do some wiggling to persuade it. I advise against prising it off with any tools, as you might bend the baseplate.

3. With the actuator removed, try to wiggle the spindle of the valve. It has only about 35 degrees of travel. It should be possible to move it just with your fingers.

If it moves freely, then it tends to indicate that the intermittent behaviour of the valve is caused by a failing actuator. If you can't easily turn the spindle with fingers, then it's sticking - you can try to wiggle it free with a tool, but don't use anything with serrated jaws that might rough up the brass surface. A small adjustable spanner is good, but don't force the valve spindle - just gentle wiggling.

If the valve was sticking the actuator motor might have become damaged, but you can turn the power back on with the actuator unmounted, and check that it operates.

Let me know if you have trouble with of the above guidance.