gas boiler

[suff]

The boiler doesn't light up on our Potterton Profile when we want hot water - but its fine when the central heating system is activated. Its worked well for years & the thermostat on the hot water tank was recently replaced. Any ideas so I don't get ripped of again?

[BillyNoMates]

Did it work OK when the HW tank thermostat was replaced ?

If it' working OK on the CH side then I would think that the boiler is OK.

Sounds like the tank thermostat is not calling for heat via its thermostat in order to fire up the boiler.

Is it a system with a 3 way valve so you can have either HW or CH, or just HW or just CH ?

[ACB312]

The answer to this really depends on your system configuration. I'll describe mine and you can maybe get enough information to make a decision. My programmer/clock says "GO" at the programmed times (i.e. applies 230V) to the tank and room thermostats. If they want heating they apply the 230V to the two motorised valves, which then activate and open the hot water flow from the output of the boiler and also send the 230V to the pump and the boiler. Your system may be fitted with two motorised valves (one pipe in, one pipe out) or a three port valve (one pipe in, two pipes out) and the tank or room stat determines output to one or the other or both. The action of the motorised valve can usually be visually checked by watching a lever on the valve moving accordingly. It may be in order to consider if your new tank thermostat is correctly wired in - if you turn the desired temperature up on the stat do you hear a click? Does the motorised valve lever move?
I can't be more precise as I don't know your system or your knowledge/capabilities of plumbing. If you can supply more symptoms I'll try to help. Cheers, Andy

[ACB312]

Oops, looks like I just crossed over posts with 'billynomates'. His advice looks good too. If this is a combi boiler then I'm sorry, I can't help, I have an old system that has been working since 1982 with only the motorised valves and one tank thermostat needing replaced in 24 years! (240,000btu boiler and 27 radiators for the anoraks).

[BillyNoMates]

No worries ACB - I know the boiler fairly well as I installed my Potterton Profile many moons ago. Modernised it with tank stat and 3 way valve etc.

But from reading your post I suspect you may be a little more experienced !

[suff]

Thanks ACB & billynomates. Bear with me here as I'm a right noddy in this field.
* its not a combi
* I can only find 1 motorised switch on the pipework near the h/water tank (silver - marked Honeywell) - I'm pretty sure there is only 1
* there is 1 pipe in & 1 out from the boiler
* the thermostat on the h/water tank does make a 'click' when turned up
* curiously the boiler 'sparked' into life briefly last night - no idea why
* it worked perfectly for years - even during the summer when the central heating was off
* I don't think there has been any difference since the HWT thermostat was changed

I'm thinking this is a motorised switch problem - as there appears to be just 1 - but can't work out why it now won't give us hot water??

Any advice most welcome

[Hard@it]

I would say it is definitely your 2 port valve motor serving the primary heating water to your cylider is requiring replacement.. Hard@it

[suff]

hard@it - would this be the 'Grundfos selectric' contraption ?

[Hard@it]

No, I may be wrong but you should have two valves, one for your cylinder control and one for your heating, and these will both be controlled by your time clock (programmer). The stat on the cylinder controls what appears to be your honeywell valve, and (if you have one) your roomstat controls the other. You will have to make sure clock is not calling for heat, and is calling for hot water, make sure that your cylinder is cold and that you have not got the Immersion on. When you are assured that all is not working - manually move the small lever on the valve alon to manual and boiler/pump should come on. If it does then it shows that your valve is not actuating and needs a new motor. I sincerely hope that your immersion has not been on all this time and holding off your hot water controls. Hard@it

[Hard@it]

PS the Grundfoss Selectri is your circulating pump. Hard@it

[suff]

Thanks Hard@it - there is definitely just 1 motorised valve. I did as you suggested & moved the lever along manually but it just returned to its starting position with no response from the boiler. Boiler starts up as soon as I turn up th CH thermostat so that seems OK. So it looks like its the Honeywell MV at fault?

[Hard@it]

Suff, glad your nearly sorted, these motors do not cost the earth. Cheers Hard@it