Central Heating - Boiler Firing, Radiators Cold

[williamsp]

Hi - I'm looking for advice, please.

We have an oil fired boiler and recently I've noticed that our heating doesn't seem to be working properly. Normally, the boiler will fire when the heating comes on and it will go off when the house has reached the required temp (around 20 degress as controlled by our room thermostat) - usually within 30 - 45 minutes. The radiators normally begin to feel warm within 10 mins of the boiler firing. What I'm seeing at the moment is that (occasionally - maybe three or four times a week) the heating will come on and the boiler will fire up as normal. However, the radiators do not get hot. The boiler continues to fire for as long as the heating is on, but the radaiators do not get warm.

Another occasional problem is that when the heating and water come on at around the same time in the morning, the heating may work but the water does not get hot. I assume this is probably related?

We had a plumber come out last week and he inspected the system. He said the electronic valve is fine and he re-mounted the pump as he said it had been fitted on an angle, which is incorrect. He also vented the pump, having confirmed it's working okay. Although the system now seems quieter, we're still having the intermittant problems mentioned above.

I suspect we have an intermittant problem with the pump. As well as being concerned that the system isn't working as it should, I imagine that we're using far more oil than necessary as the boiler is continuing to fire with little or no effect? Or am I misunderstanding what is happening here?

Any advice gratefully received.

Thanks - Paul.

[arif]

Hi

We've had the same problem before.

One of the things to test first is to switch off your heating system from the boiler control panel and then just turn on your hot water tap. If after turning on the hot water tap you notice that the radiators feel a bit warm this means that there is a problem with the divertor valve. The work around was that we flushed the entire system including leaking the water out of the boiler and filled it up again to a bare minimum level and then after a few hours it worked.

Hope this helps.

Regards, Arif

[e-mail] wrote:

[Roger Mills (aka Set Square)]

You seem to be assuming that the OP has a combi boiler - which he didn't say he as - and almost certainly doesn't have. So your solution is not relevant.

[williamsp]

You're correct Roger - it isn't a combi-boiler (thanks anyway for your suggestion, Arif). Any other ideas, anyone?

Thanks again....

[Roger Mills (aka Set Square)]

We need to know a lot more about the way your system is controlled to be able to make any sensible suggestions. Is it fully pumped, or gravity (convection) HW and pumped CH? [Clue: how many water pipes are connected to the boiler? What size are they, and where do they go?] How many motorised valves are there, and what type? [If system is fully pumped, there will likely be one 3-port valve or two 2-port valves]. Is there a thermostat strapped to the HW cylinder? (not the one incorporated into an immersion heater, if any).

As a general point, if the boiler comes on but the radiators don't get hot, it means that no water is flowing through them. This could be for any number of reasons, including:

• faulty room thermostat (which thinks that the heating doesn't need to be on, so the boiler is running just for the benefit of the HW)

• faulty zone valve

• faulty pump

• air-lock or blockage

If the boiler is purely keeping itself warm but not heating the HW or radiators, it will be wasting energy - but not using as much it would when there was proper circulation.

[meow2222]

The most likely problem is the 3 port valve, less likely is the controller that controls it, or the wiring to it. Metering the controller output or valve input will tell you which.

For peace of mind I'd check the boiler isnt boiling, as if it is there would be a danger (plastic header tank boiling and collapse). Its unlikely.

NT

[williamsp]

Thanks for your responses guys, and sorry for the delaying in responding. I took the cowardly way out and called a plumber. I was lucky enough to find a superb OFTEC engineer who I'd recommend to anyone - let me know if you want his details.

So, here's the story of the fix....

As stated in my original post, he suspected the pump as the original installer (whom I'll also supply details of if required - so that he can be avoided) had installed it on an angle which I now believe can cause premature wear. He'd also fitted a larger pump (15/60?) and set it to speed three - far too much for our small-ish three bedroomed house, apparently. So, as the re-mounting of the pump hadn't helped, he replaced it. But, this had no effect, unfortunately.

Secondly, he went to the boiler and realised that even though the fan was spinning (that's why I assumed the boiler was running), it was only firing intermittently. In this situation, apparently, the boiler should 'lock-out' but this wasn't happening. The suspect component was the control box. He spent an hour or so looking at this and finally opted to fit a replacement. Two issues were identified when fiiting the new control box - 1 - the new box hadn't been supplied with a new PCE (is this correct? Photo- something or other) so the old one had to be refitted, and 2 - the old box had been wired incorrectly, preventing lock-out and causing the solenoid to burn up quite badly. So, a replacement solenoid, too. Still no joy - further testing identified the PCE thing as the most likely culprit.

So, next day, armed with a new PCE, the boiler eventually fired correctly each and every time. We now have heat!

The plumber has offered to remove the new pump and control box for no cost as they weren't necessarily required. However, I'm not keen to store potential problems for the future so I'm happy to pay for these and for them to remain. I have to say, too, that the overall bill for his labour was MUCH lower than expected. He spent 3 hours on the first day investigating and another 1.5 hours on the second finishing the job. He supplied all the parts to me at cost price to him, too.

Finally, two further issues - he found the original boiler commissioning document in the owner's manal. It hadn't been completed or signed. He's also noticed that the pipework leading from the boiler is of a narrower gauge than required and both pipes had been fitted to the same side of the boiler, which means we have no cross-flow. He suspects that this is why the larger pump was fitted and set to maximum speed to compensate.

Amazing, isn't it? He's coming back in a few weeks to commission the boiler (it's been installed for 7 years...), fit the correct fire valve outside of the garage where the boiler is located (the current one is actually inside the boiler casing - not much use if there is a fire) and complete the relevant paperwork. At this point we'll be on the way to having a correct installation.

So, every cloud has a silver lining. We have a much improved, working heating system now and an excellent contact for servicing work in the future. My wallet is a bit lighter, but not as light as I feared it was going to be!

Thanks again, all.