Hot Water only working when Heating on?


Postby Ianm1973 » Tue Nov 09, 2010 3:25 pm

Hi all,

I have a Bosch Greenstar system boiler with a ariston pressurised cylinder and been having an issue with my heating system for some time. Its been going on so long that i cant remember when it started. I had a potterton boiler before and that also had the same issue so it cant been the boiler.

I need to have the Heating on to enable the heating of the hot water tank.

On the programmer if i click on the "hour" button for heating the light comes on and the boiler fires up for and hour and heats the house. Howerver If i click on "hour" button for the water the light comes on and nothing happens, the boiler does no ignite? Therefore the only way to get hot water is to have the heating and water on together.

Would say this is not to pleasent in the summer however the rasiators have thermostats on so not been an issue until this week when now the hot water does not seem to be heating even though both lights for water and heating are on.

Can someone advise what the issue is likely to be so i can get the appropriate person in?

Electrical fault - Wiring issue? programmer not wired up right? Has no been touched?

Motorised valve issue? - How do i check they are working - i have two of them next to the cylinder in the loft?

Many Thanks

Ian
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Postby stoneyboy » Tue Nov 09, 2010 10:31 pm

Ianm1973,
You need to check that the MV controlling the hot water is working. If you select hot water only, the manual lever should become free.
end
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Postby Ianm1973 » Wed Nov 10, 2010 12:29 pm

Hi Stoney, Thanks for the reply

I have switched on Hot water for 1 hour (boost) and popped into loft and both MV's are still moveable (hear motor turning - not Loose) and the boiler does not kick in. I moved the levers manually and still not action from the boiler? Would this point to an electrical issue?

thanks

Ian
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Postby Ianm1973 » Wed Nov 10, 2010 8:02 pm

I just switched the heating on for one hour and one of the motorised valves became loose so presuming that this valve is for the heating and the other is for the water.

When i click on the hot water only on the programmer what should happen? Would it be the microswitch in the valve? What fires up the boiler?
Ianm1973
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Postby musical2 » Wed Nov 10, 2010 9:15 pm

[quote="Ianm1973"]Hi Stoney, Thanks for the reply

I have switched on Hot water for 1 hour (boost) and popped into loft and both MV's are still moveable (hear motor turning - not Loose) and the boiler does not kick in. I moved the levers manually and still not action from the boiler? Would this point to an electrical issue?

thanks

Ian[/quote]

I don't know if this helps but I had this problem with a combi boiler. I was in a rented flat so it was down to the landlord. The heating engineer had to replace a circuit board in the boiler to solve the problem.
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Postby plumbbob » Thu Nov 11, 2010 9:15 am

Switch everything off and operate the manual lever of each valve in turn. They should feel identical. A correctly working valve will have a fair resistance and should run slowly but smoothly to the end of its travel. As soon as you release the lever it should return fully to rest.

Any indication of jerkiness or staying very loose would point to a failing valve.

It is the valve opening that triggers the boiler so if it is seized partially open, that would explain why the boiler fails to operate.
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Postby mraich » Tue May 07, 2013 7:51 pm

Not sure I am doing this correctly but I have a similar problem with my BAXI Combi Instant 105HE system. When I turn the hot water on the water heats up for 30 seconds or so then it goes cools again. Same when I am in the shower but it seems to heat up then go cold and then heat up again. Any suggestions on what might cause that?
Thanks
mraich
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