Central heating switches off after 30 minutes - why?

[stephc]

OK, in your case, yes, the hex head does seem to be the central screw I meant.

Have you ever turned the pump valves above and below the pump?

When I turn the hex head there is a lot of water coming out. Thought it was just supposed to be a dribble?

 

[JohnD]

that suggests the end bearing is worn out. Suggest you replace the pump. Sounds like you have a sediment blockage in the downstairs pipes. Hold a magnet against all accessible pipes, especially T joints and elbows. It will be attracted to sediment clumps because they are black iron oxide (magnetite). If you are unable to clear them (possibly cutting out and replacing blocked sections) you will need professional help. If the pipes still get warm you have not (yet) got a total blockage so the chemical clean can still get through.

Clean the system because sediment will wear out the pump bearings. When you take the old pump off, see if its ports are blocked or it shows other signs of corrosion or wear.

If the pump valves are still in working order (doubtful) you can change the pump without draining the system. Grundfos is a good pump brand. If you are short of money you can often find them second hand where a boiler has been renewed, but it's a gamble.

 

[stephc]

that suggests the end bearing is worn out. Suggest you replace the pump. You still need to try bleeding the highest rads to see if water squirts out forcefully.

Clean the system because sediment will wear out the pump bearings. When you take the old pump off, see if its ports are blocked or it shows other signs of corrosion or wear.

If the pump valves are still in working order (doubtful) you can change the pump without draining the system. Grundfos is a good pump brand. If you are short of money you can often find them second hand where a boiler has been renewed, but it's a gamble.

Is Wilo any good? https://www.screwfix.com/p/wilo-ssrs2501-replacement-central-heating-pump-230v/5082v

 

[JohnD]

AFAIK not as good as Grundfos, but as you've noticed, they are expensive.

Not trying to be rude, but are you strapped for cash?

edit
I am not a pro, but it looks to me like you have the (dark red) shell of a Grundfos pump that has had a (blue) replacement head (the part with the motor and impellor) fitted to it as a partial replacement. The head may have been a budget part.

 

[stephc]

AFAIK not as good as Grundfos, but as you've noticed, they are expensive.

Not trying to be rude, but are you strapped for cash?

edit
I am not a pro, but it looks to me like you have the (dark red) shell of a Grundfos pump that has had a (blue) replacement head (the part with the motor and impellor) fitted to it as a partial replacement. The head may have been a budget part.

Yes I'm poor! Maybe you're right there, only been in my house for a year so not sure.

 

[JohnD]

When I was hard up, I once got a second-hand pump very cheap, where the boiler had been replaced by a combi. It even came with the used pump valves.

I just had a look on fleabay, used, they vary from £9.99 to £25, but you need one local to you to save postage costs. Some come with a 30-day guarantee.

Look for any specification numbers on the label of yours. You need a red one, not one from a combi.

The "130" or other suffix relates to the physical distance between the ports, so a new one fits straight in without needing to change the pipes. The 15-50 or other numbers relate to the head or power

(a professional may come in and explain better or more accurately. Maybe one local to you will offer one.)

 

[stephc]

I'm going to tackle this tomorrow by draining the system, and putting in some x300. Can I put this straight into the f&e tank or is it better to go in one of the radiators? If this doesn't help I'll install a new pump.
Thanks for all your help John, much appreciated.

 

[JohnD]

X300 is for new systems.

Yours is an old system.

X400 is for old systems.

Start by cleaning out the f&e tank.

 

[JohnD]

https://www.diynot.com/diy/threads/...snt-flow-when-heating-on.489033/#post-3989998

Read this link

 

[stephc]

Sorry I meant x400. I only have 3 rads in the whole house as it is a very small one bed. So won't need much of it.

 

[Twenty Four]

Have you checked your boiler isn’t turned right down?

 

[stephc]

Have you checked your boiler isn’t turned right down?

Yes it's on max. It works fine for 30 minutes then goes off. Potterton model. Amber light constantly on so it's calling for heat.

 

[DaveHerns]

When you say it goes off , is it turned off by the room stat or is the boiler overheating and cutting out?

 

[stephc]

When you say it goes off , is it turned off by the room stat or is the boiler overheating and cutting out?

Overheating and cutting out. Not touching thermostat

 

[DH6]

Sounds like you have a dirty system and the boilers main heat exchanger has become partially blocked/restricted.

Are there any noises before the boiler goes off?