Boiler problem

[DIYSB]

I'm not bad at basic plumbing, do all my own radiator installations, pumps etc but have a problem I can't solve.

I have a system boiler not a combi, its a Gloworm. When there is a demand for hot water only the boiler comes on for a short time and goes off. When there is a demand for domestic hot water and central heating it works fine and I get hot water in both systems. Originally I thought it was the old themostat on the water tank and changed it for a new one. That didnt work. I have changed the old pump as a part of a preventative maintenance programme so thats the not the problem. Thinking it could be the boiler I had it serviced with a clean bill of health. The guy that serviced it investigated the problem and said he was sure it was a faulty diverter valve which was 18 years old. So I bought a new Honeywell power head for the valve and fitted that, checking at the time that the valve was actually moving into all 3 positions (Water / CH / Water & CH) which it was. The problem though persists. It's as though when there is a demand for water only the valve isn't opening to that position but as I said I have ftted a brand new powerhead on the 3 port diverter valve. I'm now a bit stumped so came here looking for some suggestions or even answers.

 

[kevplumb]

plan ??
y plan
w plan
s plan

 

[picasso]

Have you fitted any type of air release on the coil of the cylinder ? it sounds like its airlocked.

 

[DIYSB]

Have you fitted any type of air release on the coil of the cylinder ? it sounds like its airlocked.

No, nothing like that. Air block would effect the water system though would'nt it, which works fine when the CH is on.

 

[DIYSB]

plan ??
y plan
w plan
s plan

Sorry mate, don't understand that?

 

[ServiceNumpty]

3 positions (Water / CH / Water & CH)

Y plan I reckon.

 

[twgas]

I would suspect OP has y plan as he mentioned a 3 port, could be W but they are few and far between these days

 

[libby lou lou]

Hi kev.

 

[tincup]

Hi

Do you have a gate valve fitted as a bypass and is it open enough?

HTH

 

[kayedee]

Did you check that the boiler and pump were being activated when you checked the valve was operating in hot water and central heating positions?

 

[Servotech]

I'm not bad at basic plumbing, do all my own radiator installations, pumps etc but have a problem I can't solve.

I have a system boiler not a combi, its a Gloworm. When there is a demand for hot water only the boiler comes on for a short time and goes off. When there is a demand for domestic hot water and central heating it works fine and I get hot water in both systems. Originally I thought it was the old themostat on the water tank and changed it for a new one. That didnt work. I have changed the old pump as a part of a preventative maintenance programme so thats the not the problem. Thinking it could be the boiler I had it serviced with a clean bill of health. The guy that serviced it investigated the problem and said he was sure it was a faulty diverter valve which was 18 years old. So I bought a new Honeywell power head for the valve and fitted that, checking at the time that the valve was actually moving into all 3 positions (Water / CH / Water & CH) which it was. The problem though persists. It's as though when there is a demand for water only the valve isn't opening to that position but as I said I have ftted a brand new powerhead on the 3 port diverter valve. I'm now a bit stumped so came here looking for some suggestions or even answers.

Change the whole 3-way valve.
Heats not getting away from the boiler when it's in the h/w only position it's what we experts call "lock out"!
servotech,

 

[DIYSB]

Hi

Do you have a gate valve fitted as a bypass and is it open enough?

HTH

 

[DIYSB]

I'm not bad at basic plumbing, do all my own radiator installations, pumps etc but have a problem I can't solve.

I have a system boiler not a combi, its a Gloworm. When there is a demand for hot water only the boiler comes on for a short time and goes off. When there is a demand for domestic hot water and central heating it works fine and I get hot water in both systems. Originally I thought it was the old themostat on the water tank and changed it for a new one. That didnt work. I have changed the old pump as a part of a preventative maintenance programme so thats the not the problem. Thinking it could be the boiler I had it serviced with a clean bill of health. The guy that serviced it investigated the problem and said he was sure it was a faulty diverter valve which was 18 years old. So I bought a new Honeywell power head for the valve and fitted that, checking at the time that the valve was actually moving into all 3 positions (Water / CH / Water & CH) which it was. The problem though persists. It's as though when there is a demand for water only the valve isn't opening to that position but as I said I have ftted a brand new powerhead on the 3 port diverter valve. I'm now a bit stumped so came here looking for some suggestions or even answers.

Change the whole 3-way valve.
Heats not getting away from the boiler when it's in the h/w only position it's what we experts call "lock out"!
servotech,

Thanks mate, sounds like good advice and fits the symptoms. I will do that but I did take the power head off again and check the paddle on the valve was moving freely to all three positions. What causes the problem?

 

[Servotech]

General wear and tare (sticking).
I almost wrote wear and tear
servotech

 

[DIYSB]

General wear and tare (sticking).
I almost wrote wear and tear
servotech

Sorry to say changing the valve hasnt solved the problem. I now have a new header unit and 3 port valve. Upon inspection of the old valve after I removed it, it did seem to be in perfect working order. I fitted the new one anyway, to be sure but the problem persists, as in the boiler shuts down when there is only a demand for hot water but works fine when there is a demand for central heating or central heating and hot water.

Really scratching my head on this one now. Any more suggestions?