potterton suprima 40 boiler problem

[pink21]

Our boiler seems to come on but goes off before the central heating reaches the temperature setting, it never stays on for more than a few minutes.
However when the hot water is on it seems to be fine. The hot water seems to override the central heating and we are having to keep the hot water on to get the central heating to get to the set temperature.
We have had a new circuit board fitted a few months ago.
Should the boiler heat setting be on maximim?
Any advise would be greatly appreciated, thinking of getting someone in but would like some ideas of what could be wrong so we have some idea of what to expect.
Also does anyone know what the recommended hot water temperature should be?

Thank you

[Hymie]

This boiler is a fully sealed system, having only one hot water outlet & return, feeding both central heating & hot water. Your hot water is achieved through a heat exchanger within a hot water tank.

I suspect your problem may be caused by insufficient water flow when the boiler is working on central heating only. With both central heating and hot water demand, there is enough flow to operate the boiler normally.

When your system is cold, feel the temperature of the boiler hot water flow & return pipes (the flow is the left hand pipe). Switch on the central heating only (set at maximum temperature), and the water from the flow pipe should become hot. The boiler should continue with the gas burner on, until the return pipe has become as hot as the flow pipe. At regular intervals thereafter, the boiler should fire up for a minute or so to maintain the central heating temperature.

What I suspect is happening is that because the water flow is restricted, the hot water from the boiler will reach the thermostat set temperature and switch off the boiler, before the return flow has even begun to get warm. The slow flow of water through the system will cool the thermostat, causing the boiler to switch on again � with the whole process repeating itself without the central heating reaching the required temperature due to the low water flow rate through the system.

If the above is what is happening to your boiler � post a reply and I will give you advice on curing the fault.

[gucciman]

sounds like you could have a faulty pump. the hot water circuit is relatively short and typically uses 22mm pipe so the pump could well be sufficient enough to pump the water round. but the central heating circuit is a lot longer, having to pump the water around the whole house and the pump may no longer have the force to do this, this would be made worse if your radiators are installed on microbore pipe i.e. 8 or 10mm. the other reason for insufficient flow around the heating circuit is sludge in the pipework/radiators. how old is your system? it may need flushing out.
as a long shot it could be a faulty room stat.
you may wish to contact baxi potterton who offer a fixed price call out, they guarantee to fix your boiler and the price includes all parts and labour. the current price is 225 pounds which you have to pay up front on your credit card and they then arrange a time to call on you. if you need something like a new circuit board or a fan then this works out as a great price as those parts are very expensive and the potterton engineers are the experts on their own boilers. not such a great deal if you only need a new pump however as that would be around a 100 fitted.
suprimas arent necessarily a sealed system, they can be used as a conventional system with a header tank for the central heating. to convert it to a sealed system an expansion vessel would need to be fitted and the boiler would have to have a overheat thermostat capable of cutting the boiler off before it reaches 100 deg c.
the recommended hot water temp from the taps is normally around 60 deg c
hope that helps, please keep us posted as to what the engineer you call out does.

[annie0000]

Does your system need vented? What does the pressure meter show?

[pink21]

Thanks for your advice so far, I will check what Hymie says before getting anyone out.

Will let you know the outcome

[Hymie]

You appear to place confidence in me without knowing whether I am competent or not to advise on this subject. Regardless of what advice anyone gives you (on this site), you should ensure you are happy with the advice and understand the reason/logic of carrying out any recommendations.
I would even invite Gucciman to comment on my response(s) (two heads are better than one).

OK, lets assume that your problem is due to a low flow around the system, Gucciman is correct in that this is likely to be due to the pump being on the way out or some blockage/restriction within the central heating section. Unfortunately even for someone looking at the system, it can be difficult to tell which. A skilled engineer might be able to recognize tale tell signs from the pump (noise/vibration etc), that it was faulty and required replacing. More likely, the engineer would replace the pump, if that did not work then they could be fairly certain that power flushing the system would work.

Gucciman recommends replacing the pump, which will cost around �100 (get a quote before agreeing to having the job done). I would recommend flushing the system first (not power flushing, for which you will have to call in an engineer). My reason for this is that you can easily do it yourself at no cost (or for the price of a length of plastic tubing). Unfortunately you can only flush the system under the water supply pressure (if a fully sealed system), or what could be more correctly termed a drain, if your system has a header tank fill/top up.

There is a further (unlikely) possibility, that your problem is caused by one of the control valves within the central heating not fully opening as it should. Unfortunately by the time you consider this possibility, you will have replaced the pump and power flushed the system.

Let us know how you get on � I�m sure that between us, Gucciman and I, we assist you in understanding the

[gucciman]

hi hymie and pink

in a case like this i would always suspect the pump first, a blockage in the system is likely to show up as some of the radiators getting warm and others not.
as you say i would check the pump to see if it is excessively hot, i would then listen to it by placing by ear on the handle of a long screwdriver and the other end on the pump body, and lastly i would remove the large screw and test to see how fast the impellor is spinning by gently touching it with a screwdriver tip. at the same time i would check to see the pump is set to the correct speed or possibly turn it up to a higher speed to see it that helps.
it could possibly be another circuit board problem, suprimas seem prone to circuit board failure, we see a lot of them, and its not rare to purchase a new circuit board and to find thats faulty too.
i really would call out a heating engineer to help you out and i'm not saying that just to protect my interests, if your not competent at this sort of thing you could end up in a mess, a very wet mess!

[pink21]

Just thought I would let you know that we have played around with our settings and the radiator valves and things seem to be working better at the moment.

First time I have had to understand the working of central heating and was expecting the boiler to be on a lot more often than it does, but having spoken to people found out that it should only come on for a few minutes at a time.

Thanks for you help though.

[zeno]

I have a somewhat similar problem in my open vent heating system with a non modulating old Glowworm boiler. The gas flow is always at the same rate. The boiler will come on in the morning for about 20 minutes of continuous firing. After that it will fire up and shut down about 15-20 an hour until the room thermostat is satisfied a few hours later. The boiler thermostat is set at maximum and it is this that shuts down the boiler. The boiler is always kettling and the temperature rise across the boiler is 30-35 degC. This suggests to me that there is inadequate flow due to system restriction or a pump problem.

When the system starts from cold it will take about just over 15 minutes to reach about 35 C at the boiler inlet and about 75 C at the outlet, when the boiler thermostat will shut down the boiler. Boiler thermostat is set for maximum. As the heating continues it will settle down to about 48C at inlet but always shut down when the outlet is around 75 C. I cannot have the cylinder and central heating at the same time because the short circuit for the cylinder means the central heating does not get any flow. The pumped flow is estimated to be 0.9 -1.2 m3/hour. I have the cylinder heating off in the morning so that room heating takes priority. I turn on the cylinder heating after midday and it is left on until boiler shuts down before we go to bed. Cylinder water is hot enough for use in the mornings. I have used an infrared thermometer that I bought through the CORGI website for about �23. It is a useful device when you are trying to balance the radiators and to measure boiler inlet/outlet temperatures. . Stick a piece of black insulating on the area of pipe you want to measure and hold the device about 5 mm from the taped surface.
I am not a central heating engineer or gas engineer, but I hope my rambling may contain information.