Boiler pressure drops when heating comes on or hot tap.

[Sponge]

I have just noticed that the pressure gauge on my boiler drops by 0.5-0.75 bar when the heating comes on, or I turn a hot tap on. When I turn the heating off/hot water off, the pressure goes back up again (1 bar).

I have been around the house and can find no leaks on any of the radiators.

The PRV is dry.

What's occurring?

 

[mfarrow]

What's occurring?

Normality.

 

[Sponge]

So it's supposed to significantly drop when it's working? It's not behaved like this before.

 

[mfarrow]

I must admit 0.75bar is a lot, it's caused by the pump dragging water through the boiler and hence lowering the pressure on the gauge side.

A sudden increase in the pressure drop could be caused by a blockage on the return side of the boiler. If you've any filters, make sure they're clean and retry.

Has the pump been getting noisier at all? Radiators slower to heat up? Hot water not as hot?

 

[Sponge]

I'll check the filter.

The boiler is a little noisier than I recall (but we only moved in in May), but everything else is fine.

 

[Agile]

So you did not bother to get the boiler serviced during the summer?

Tony

 

[45yearsagasman]

Maybe it was serviced just prior to moving in?

 

[Sponge]

Woah, there! Making assumptions aren't we?!

We paid for a gas inspection before we bought the property. The boiler was also given a clean bill of health by the previous owner. It is 2 years old and had a service history.

I also had the boiler serviced as soon as I moved in! (With no issues detected.) I have a boiler service contract and it was compulsory for switching the account from one address to an another. (Effectively a new contract.)

But the boiler spent most of it's time off since then; only being used intermittently for hot water. On top of that, we moved out for 6 weeks during the rewire. So it's only now it's being used a lot more (heating is on) that I've noticed the drop in pressure and, possibly, more noise.

Some of the noise is due to the lid vibrating. (Yes, it's screwed in.) It reduces when I hold it. But that may just be a symptom of whatever is causing the vibration in the first place and that is (possibly) the issue.

 

[Agile]

Gas safety inspection is just that. Not a performance check.

I would never trust the seller of anything to give a valid opinion of anything!

But with a service contract you should be OK.

Noisy resonant casings are not likely to get much of attention from them though.

Tony

 

[Nozzle]

Does the gauge measure the pressure of the heating/coil circuit, or the incoming mains water?

If the later, then you should expect it, as there is a pressure loss through a pipe when fluid flows. If it's the heating/coil circuit, then maybe you have a leak through the cylinder heat exchanger.

Nozzle

 

[Sponge]

I don't know. It's a Vokera Compact 25.

It appears to be getting worse. Now I'm losing pressure. I noticed a slight drop in pressure this morning, so topped it up to 1 bar and it's now dropped to 0.6 bar.

I've been around the house again and can find no leaks from any of the rads.

It might be time to call NPower out.

 

[Nozzle]

Ah, if you topped it up via the filling loop, then it is the heating/hotwater loop, rather than the actual water from the head tank. There is a chance that it is loosing pressure through the coil itself. If you don't run any hot taps for a while and watch the overflow pipe. If water issues forth, you've found your leak!

Nozzle

 

[Sponge]

I'll do that, thanks.

In case it has any bearing on fault diagnoses - I topped the system up to 1 bar last night and this morning, 0830, it had dropped to 0.7 bar. No hot water usage and heating comes on around 0630.

Between 0830-1130 the pressure dropped from 0.7 - 0.2 bar (a greater drop than overnight). And that's with morning showers and heating on.

 

[Sponge]

The following may be unrelated, but I'd like to explain what's happened over the last couple of days and where I am at the moment.

I've still been losing pressure. I top up the boiler to ~1.2 bar last thing at night and by the morning it's dropped to zero.

I went around the house again, checking for leaks. Only this time I took my bleed key and checked for air. All of the radiators were hot to touch, but I checked them anyway.

Downstairs was fine. Upstairs was a different story.

I have three radiators (2 of the bedrooms and the bathroom), each of them had significant amounts of air in them (although none of them were particularly cold at the top). I bled them and refilled the system to ~1 bar.

The pressure was still dropping over time.

I bled the radiators a little more. Topped up. Still drops in pressure.

Now there was no air left to remove.

It was about this time that we lost pressure in the cold water in the kitchen. The supply for the kitchen branches off at a pushfit Tee just after the main stop-cock. It's a single JG barrier pipe which goes from under the boiler (in kitchen), under the floor and re-emerges on the other side of the kitchen. This pipe has Tee's for dishwasher, sink, washing machine and finally terminates with the outside tap.

The sink tap hot (different supply pipe, obviously) was fine. The sink tap cold was slow. The outside tap cold was slow. The WM wouldn't turn on (error message: no water, check pressure/connections). The DW worked, but seemed slow to fill (although I'm not 100% on this).

The other taps in the house were all fine.

So, I had a blockage somewhere in the pipe supplying just the kitchen.

I was at work, so asked my dad to pop over and troubleshoot.

He disconnected a few pipes. Swapped over a few. And was coming close to the conclusion that yes, there was a blockage reducing the flow somewhere in the pipe from the Tee just above the stop-cock and either at, or just after, the appliacance Tee for the DW.

Before proceeding to the next step of trying to flush the offending pipe, he (for some reason) decided to reconnect all the pipes and it was at this stage he tried the tap again and it was fine! The flow was back to normal at sink tap and outside tap.

It was late, so he left it as-is for me to continue today.

Anyway, I texted him just before he left my house (did I mention I was at work all day yesterday?) to ask him what the pressure was like on the boiler. He replied, it was a zero. He topped it up, but to 2 bar. (He admits this was too high.)

I got home last night and decided to drain the system a little. I thought I'd kill two birds with one stone and emptied the TF1 filter. The first flush was black. Full of small black bits. The subsequent 3 or 4 flushes got clearer, until it was a pale beige colour, with just a few black bits in. The pressure was now ~1.4 bar.

I left it at that, fully expecting to find the boiler back at zero bar this morning.

So, imagine my surprise when I checked the boiler at 7am to find it was at >3.2 bar!

I haven't checked the PRV yet, but I expect to find it dripping.

I'm sorry if I've gone on a bit. And congratulations if you've got this far. I'm totally confused. It's gone from one extreme to the other.

 

[Boilerman2]

As your boiler is under a Service Contract, why have you simply called the Service provider! Surely this is what you are paying them for?