Please help with Potterton Netaheat Profile

[Ronald0]

Hi, my 15 year old Potterton fires up fine but shuts down after 8 mins so will not adequately heat the rads. With hall stat still calling it will refire after 20 mins and shut down after about 8 mins and so on.

When my engineer visited he said the boiler is locking out because the return temp is too low compared to to flow temp and reckons there is a circulation problem. The over heat stat is not tripping, it is shutting itself down on the boiler control stat.

He has fitted a new pump, flushed the system (but not power flushed) but has not fixed the problem. He is coming back to take off some rads.

Thinking this through, if I shut down the hall stat to shut off the rad circuit as it would be in the summer, and the cylinder water that comes out of the hot tap is hot then with the cylinder stat only calling the return temp to the boiler would only be slightly lower that the flow temp so what he is saying may not be accurate.

In this situation the boiler behaves exactly the same. So I have moderately hot water but hardly any heating.

Thank you very much for any help.

 

[45yearsagasman]

Faced with a situation like yours, I would not take off some rads!
I am presuming you have a fully pumped system (you tell us little) so I would concentrate first on the pipe work and zone valves etc near the pump and cylinder. If your system differs from this the give more info. It is almost certainly a circ fault. I am assuming that your boilers controls have been checked by your man and proved to be ok. No offence, but his name isn't Wally is it?

 

[Ronald0]

Faced with a situation like yours, I would not take off some rads!
I am presuming you have a fully pumped system (you tell us little) so I would concentrate first on the pipe work and zone valves etc near the pump and cylinder. If your system differs from this the give more info. It is almost certainly a circ fault. I am assuming that your boilers controls have been checked by your man and proved to be ok. No offence, but his name isn't Wally is it?

Thank you 45years. System is a fully pumped conventional system with F and E tank in loft, there are two separate motorised valves either side of a tee just after the pump. They are working OK as when hall stat calls, m/v opens and hot water heats pipe further up. Same with hot water circuit. Is this boiler smart enough to compare flow and return temps and lock out. Does lock out mean its trips its overheat thermostat? (which it doesn't). Boiler will refire on its own 20 mins after burner shuts down.

Boiler does not interlock with hall or cylinder stats. Could boiler control stat be malfunctioning and shutting boiler down too soon, it is set to max.

Many thanks

 

[45yearsagasman]

That boiler is simple and does not compare flow and return temps.
The overheat protection (when activated) stops even the fan from operating.
The stats on those boilers normally fail the other way and cause overheating faults.
It is very difficult from here to determine whether or not your boiler is ok without doing some on site tests. Electrical components can fail after running for a while and then resume after a cool down period. It may be time to call in someone who specialises in breakdown repairs.

 

[Agile]

Its almost certain to be a flow issue.

You can get an idea by measuring the flow and return temps when the boiler is firing.

Tony

 

[HERTS P&D]

It's not an air lock near the cylinder is it? Did your plumber bleed everything when he fitted the new pump?

Andy

 

[petertheplumber12]

you say thermostat is at maximum, try turning it down to half way, if boiler behaves different, stays on a shorter time, than before then I believe you need a new thermostat, but whatever you do find a different boiler man, gas safe, not a plumber, he hasn't got a clue, some electrical test need doing. go to gas safe web site, look for an engineer, put in your post code and phone a few.

 

[Ronald0]

petertheplumber12,HERTSDRAINAGE2010,Agile,45yearsagasman,

Gentlemen, thank you all very much for your help.

Having re bled all rads I located the cylinder coil upstand bleeder and bled the hot water circuit. Also for some reason the bypass valve had been opened right up, (not by me) probably during the summer and water returning to the boiler was too hot thus shutting down the boiler prematurely.

 

[HERTS P&D]

So is it working correctly now?

Andy

 

[Ronald0]

Well yes its working as far as there is reasonable heating and hot water available now. I can live with it but the boiler is not interlocked with the room and cylinder stats as it used to be.

The connection is there in so far as I can shut off and refire the boiler with the room stat at lower temperatures but with the room stat set to 18 degrees the boiler will shut itself off before that temp is achieved. Even with the boiler control stat set on max the boiler shuts itself down too soon. I don't have pipe temp gauge but placing my hand in the boiler return and comparing it to the flow temp it is not too high.

Thank you for asking.

 

[Agile]

There should be about 11 degrees difference between flow and return at the boiler.

The open bypass would have resulted in a very small differential at the boiler and little heat to the rads.

Tony

 

[petertheplumber12]

I presume the bypass is a gate valve, in which case I would try having it closed and then open only 1/2 a turn, the automatic ones are much better.