Potterton Profile Boiler starts 20 mins & shuts off 15 m

[chiligee]

Hello.

I have an issue with my potterton profile boiler - gravity system (not combi).

I better give some history about this.

about 9 months ago, the boiler packed up. I ended up changing the PCB - the circuit board with a refurbished one from the local merchant. Gave him my PCB and he gave me a working tested one. Cost me about £30.

This was following the advice of a corgi engineer i had called to check the system. He also mentioned one of the zone valves was stuck.

I decided to change the pump, and 2 new zone valves. Put in the replacement PCB, boiler fired but just for a short while. Called the engineer again, he brought ANOTHER PCB and then it worked fine - lesson is that refurbishd PCB's can go dead again!

Now recently the radiators were not heating up properly, with cold patches in the middle. this happened to only 2 of the 5 radiators in the flat.
After reading the forums, it was time to flush the system. I removed the 2 radiators and manually flushed using a hose, quite a bit of greasy black water came out.

put the Rads back, and filled the system with Sentinel X400, and filled up the system again. bled all rads and fired up the boiler

this is where the problem starts. The boiler will run for 20 mins on setting 2-3 (a knob on the boiler), and shut down , then after another 20 mins, it will start up again.

the same engineer who came before advised me to check for air lock and the pump. checked the pump, it spins fine- opened nut and put screwdriver in. there was no air escaping from the pump when i did this. Bled the rads but no air. Thermostat is set to maximum and i checked by opening it, the contacts touch.

Im a bit puzzled about this. Does this mean a boilerdoes not run constantly when switched to ON? I did notice on the central heating tank that the water is warm, hot water comes into the tank via overflow.

any recommendations?

 

[JohnD]

hot water comes into the tank via overflow.

you have a blockage (unless the pipe layout is wrong)

possibly a seized or broken valve, it might be one of the pump valves or your zone valves not fitted correctly or something else you have worked on. If you take the pump off you can look up the valves when you turn them to see if clear.

you may be able to work out where the blockage is by feeling along the pipes to see which are warm and which are cold

Is the X400 still circulating? has the circulating water gone inky black? how long has it been in? 4 weeks is the ideal period before draining and flushing.

X400 will loosen sludge but if you have an actual blockage the chemical does not circulate through that pipe so will not remove it.

If the blockage is of black iron oxide, you can detect it by holding a strong magnet to the copper pipe. It will be attracted where there is a mass of black iron oxide inside. If you have such a blockage you will have to cut it out and repair with new pipe. The sediment can go very hard and immovable.

have you got microbore?

how hot are all the radiators getting?

another possible cause of the overflow is that your pump is turned up too high for your number of radiators, or they are all closed down too much and you do not have one permanently open near the room stat.

A boiler does not have to fire constantly. It fires until it is hot enough to open its thermostat, then stops until it has cooled down a bit (mine has a 20 degree lag) so if you have not got a lot of radiators, the heat held in the water and that big iron boiler will take a while to dissipate.

 

[Agile]

Hello.

I decided to change the pump, and 2 new zone valves. Put in the replacement PCB, boiler fired but just for a short while. Called the engineer again, he brought ANOTHER PCB and then it worked fine - lesson is that refurbishd PCB's can go dead again!

Yet another example of why not to buy dodgy PCBs!

Your boiler is meant to cycle and it may well be totally correct what its doing.

However, to find out it is necessary to measure the flow temperature and see what temperature it turns off at and what temperature it comes on again.

Only by knowing this will we know if anything needs to be done.

Tony

 

[chiligee]

Many thanks JohnD,

First i had better reply to your questions.

1. Zone valves.
When i put new zone valves, it was asmost the same price to buy only the mechanism as well as mechanism plus the valves.
I purchased the full lot as can be seen in this pic. i purchased two of these for both zone valves even though the engineer said one is not working

http://www.plumbworld.co.uk/honeywell-v4043h-2-port-zone-763-1365?CAWELAID=205023804

2. Pump
Purchased the Grundfos 15-60 Domestic Circulating Pump as can be seen here

http://www.screwfix.com/prods/67637...ng-_-Grundfos 15-60 Domestic Circulating Pump

With 2 new gate valves as it was recommended to change the old ones... would be easier to fit.

3. X400 Sentinel
This was put in last week 10/01/2009 so best i leave this running till at least 10/02/2009 and report any result change.

4. how hot are all the radiators getting?
The Rads get heated quite OK after I flushed the cold patch radiators but its not the same as in other houses. I should not say luke warm, as they are on the hotter side,but not as hot as i have experienced in other houses. All the radiators do go warm.

5. another possible cause of the overflow is that your pump is turned up too high for your number of radiators
The pump is set to number 3, the highest so possibly this could be the cause. I have very few rads; 3 single rads and 2 double ones, fairly small as its a 2 bed flat. I shall try to bring the speed to 1 and see if there is any improvement.

6.have you got microbore?
I dont have a microbore actually.

I will definately reduce the speed of the pump and see if this improves the heating. I will also follow the copper pipes and see if there are any cold spots. I can only follow the 22mm pipes in the loft and check the 15mm pipes coming into the Rads (which do get warm). its a concrete floor so hard to check the rest of the pipework.

One note is that when the heating did start - boiler fired- the water in the pump got really hot, my deduction being that water has heated to max allowed and is waiting for the water in the rads to dissipate heat , once it cools down, boiler detects this and fires again to heat up central heating water.

At another place i have seen boiler stayin on for quite a long time before cutting out, unlike this 2 bed flat. I am fingers crossed that the x400 would clear any sludge for smooth flow, but i will check for cold spots, & update this post.

I appreciate your help - kindly let me know if there is anythign specific to check as well... i shall update here.

Thank you

 

[JohnD]

4. how hot are all the radiators getting?
The Rads get heated quite OK after I flushed the cold patch radiators but its not the same as in other houses. I should not say luke warm, as they are on the hotter side,but not as hot as i have experienced in other houses. All the radiators do go warm.

you can buy or possibly hire pipe thermometers, but as a rule of thumb, the flow pipe coming out of your boiler, and the flow pipes going into your radiators, should be "too hot to hold" and the Return pipes coming out of your radiators and going into the boiler should be "too hot to hold for long"

You can adjust the lockshield valves to achieve this.

While you are using X400, it might be helpful to open all the lockshields to promote high flow and stir up the sediment. Someone more skilled may comment on this.

If you ever find the pump is very hot (hotter than the pipes going into it) then the pump is stalled or jammed or circulation is blocked in some way

"Pumping over" is very undesirable as it aerates the water and causes the radiators and boiler to rust and corrode inside.

 

[Agile]

While you are using X400, it might be helpful to open all the lockshields to promote high flow and stir up the sediment. Someone more skilled may comment on this.

No, you should not do that as it starves flow from the others ( assuming they were properly balanced in the beginning ).

What is advantageous if you have some radiators where the flow is poor, is to close the "hot" ones for the first day or two to use the full strength of the chemical where its most needed.

Its pointless adding X400 if its pumping over!

Tony

 

[chiligee]

Went back to the flat, reduced the pump speed to 1 as i have a few radiators - following recommendations at this forum.

However, i have another puzzling issue. I decided to bleed all the radiators just in case.

There are two radiators which when bled, do not remove any water or air - but they are hot.

The whole house has had an improvement after just a week of x400 running. All rads are hot, with some just a bit less hot so i reckon after a few weeks, things should be much better.

What could be a reason where no water comes out of the radiator when bleeding yet its hot? implying water is passing through ... could there be some sediment or something blocking the bleeding valve?

Any suggestions?

 

[steve32]

15 60 pump with 5 radiators is over sized you need a 15 50
when you vent are you leaving pump on or turning off
if pump is on it can suck air in system when venting rads if pump is off and still no air or water you may have a blocked air vent, towel and pin will clear blockage pin to clear air vent towel to mop water

 

[JohnD]

if the X400 has been loosening black sludge and improving circulation, you might consider fitting a Magnaclean. I guarantee you will be amazed and delighted at how much black sludge it traps out of the circulating water. It continues working permanently (but does not loosen existing hardened deposits, only black particles carried in the water)

You have to drain the X400 after about 4 weeks as it starts to lose its power. Hopefully a lot of loose sludge will come out with it when you drain and rinse.

 

[Agile]

X400 only loosens the sludge!

Its part of the procedure to drain all the suspended dirt off after 4-5 weeks.

If its left any longer some of the suspended dirt starts to resettle.

X800 does all this in two hours!

Tony